Great, thank you. I’m not so successful with changing footprints yet 
As you can see in the image I placed a downloaded USB Micro female connector and cut the overhanging part on the left in the footprint. So in the 3D model everything looks fine.
But somehow the footprint is designed too tight so that I get a bunch of electrical errors (see arrows). Do you have a better footprint for me or can you recommend me a website where I can download some? Mine is from Snap Magic (snapeda.com).
Hi @Martius108
1st comment: A new problem deserves a new topic. I’ve moved the post.
2nd comment: This is a socket. It will be used; often. It needs to be as robust as possible. The bigger the copper area on the PCB, the more chance the socket will survive a lot of use.
3rd comment: The DRC complains only because you have broken the rules you have set in the Board Setup.
You have three choices: Ignore your rules (if this footprint is feasible and workable), change the footprint, or change your rules in the Board Setup.
If this footprint is as large as possible, to make the socket as durable as possible, leave it there (there is a reason the footprint designer designed it this way). This leaves; change your rules for the DRC in the Board setup, or ignore the DRC complaints.
JMHO 
In KiCad Connector_USB.pretty library (I have KiCad 7.0.11) I see 16 footprints with name starting from USB_Micro-B_… . No one is good for you that you are looking for the other source?
I have never searched any else for footprint than in KiCad libraries. If there are no what I want I select the most similar to what I need, copy it into my library, rename and modify.
Some of those errors are due to the grounds not being connected. I assume you will use a copper pour to connect the GNDs could you do that then run the DRC and show the actual errors please
Yes, I use a copper layer on the back side. After working around for a while I got out with no errors
Thank you! As a beginner in KiCad it is still not so easy for me to find the suitable footprint. On the other hand I thought it might be a good idea to get the footprint directly for the supplier of the parts. But maybe not
Now I use a Molex footprint for the USB Micro Type B female connector from within KiCad but I couldn’t find a suitable 3D model. Which is strange because there are standards for the connectors, right?
I search KiCad library for footprint may be once a year so I also don’t know libraries. At first (it was KiCad V4) I looked through libraries to roughly knew them but with each main version number change (4->5, 5->6, 6->7, 7->8) libraries change a lot.
Why I didn’t point you the probably correct footprint but only said that I see there 16 with potentially good names - because I did it with file browser based only on footprint names (not seeing them).
All symbols in my libraries have footprint assigned. So when I place symbol at schematic I have nothing to do with its footprint.
When I am searching for a new footprint I select (by file names) some of KiCad footprints and copy them (with file browser) into my library to be able to see them (I don’t see KiCad libraries). Then (in KiCad) I delete all of them except one I left to be used.
Before I moved to KiCad I even didn’t get an idea to have 3D models. So for about 30 years I was designing PCBs not having 3D models. Now I use models only to be able to make photo-like view of my PCB and insert it into documentation but practically no one needs it. To make such view I can use any not perfect model (even its pins go through PCB not when the holes are you don’t see it at top-view ).
What for do you need 3D model?
How footprint have to be made you should find in datasheet. Until you don’t want to use 3D PCB model to for example design a case for your PCB, 3D models are not needed, I think.
Are you sure there is no model?
USB3076 - USB 2.0 Connector Micro Horizontal Receptacle (socket) (gct.co)
This is the first time I design a PCB with SMDs. This is the first time I ordered such parts. So I just want to be sure that everything fits together. Of course I don’t need 3D models …
No,the bit that connects to the connector is standard of course, but the external shell, how the pads are positioned how the physical shell is attached to the PCB etc. are very non standard.
Be 100% sure you have the correct footprint laid out, and of course one tool to help here is get the correct 3D CAD and make sure everything aligns to your footprint. If the 3D CAD is not available you are a bit stuck . . . then just quadruple check your footprint to the datasheet.
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