Mouse bites are a part of panelisation, and this is one of the parts where KiCad is not very advanced (yet 
)
There are different attempts to improve this, and the script mentioned in the post below looks interesting:
https://forum.kicad.info/t/tool-for-creating-panels-in-pcbnew/15626
If you want to do it by hand, or can not use scripts, then you can use your mouse-bite footprint and modify it.