What does patch apk mean?

[Petomai]

"Patch the game client apk using apk-mitm"
I don't understand. Does anyone have a video on this procedure?
Reference link

Edit:
I think I understand, maybe, but how do I find the path to the apk? In termux ls results in permission denied, so I'm working blind. Do I use something other than termux?
Edit2: I've managed to locate the apk location using lucky patcher. I installed java 8 to termux, proot and apk-mitm but it fails on encoding apk (tried AAPT2 and AAPT) not sure how to proceed. Will try again later. If anyone can help I would appreciate it lots. Does this need to be done from a Linux x86 machine? I'm trying on my phone (ARM) hmm. Will try again later.