Hello
I downloaded UCB C footprint CX90B1-24P from here but after I use it then my whole at 3D preview is yellow and missing bottom layer.
How can I fix this footprint? It also has no 3D model included and after add path to step then it require some offset, rotation tweaking. Then is there a way to auto fix this kind of issues in the future?
I use kicad by 2-3 days so I do not know many things yet.
Experiment a bit with 3D Viewer / Preferences / Display Options
You have probably changed some of these settings and forgot about it.
For example, when Realistic Mode is turned on, the PCB usually looks green, except when you turn off the solder mask layer, because then you the yellow copper underneath.
If you also turn off the Board body, then you can look inside your PCB and see the inner layers and vias and such.
Might be a problem with either the model or the Snapeda export function. I would suggest that the first thing to do would be to jopen it in FreeCad and resave as a step model. This seems to fix quite a lot of problems especially if you use @maui StepUp workbench. @NatashaABaker is often around on the forum - she is from Snapeda and might be able to help.