Tips on Modifying PCB layout?

[Will_I_am344]

Hi! I found a keyboard I really like (Lily58) https://github.com/kata0510/Lily58

However, I want to modify the layout slightly (remove the top 2 outer buttons and add thumb buttons)

I downloaded the pcb and schematic files to KiCAD and checked them out but I am not entirely sure how to proceed with applying the changes I want. Can I get some tips please?

[controller-works]

You will need to research as much as you can on KiCAD, and keyboard PCB design. You will also need to back fill any knowledge you are missing on circuits. These will get you started.
https://github.com/ruiqimao/keyboard-pcb-guide
https://matt3o.com/book/
There are also many tutorials on YouTube if you search there.