I need help :(

(I should say I'm trying to do it on a Chromebook) I'm trying to make a gacha FNAF singing battle, but I don't really know how to use KINEMASTER, so I make them weird. I don't know how to add audio to the recording, so what I end up doing is playing the audio on my phone as I screen record the part of the singing battle I'm working on. Well I learned today, that KINEMASTER doesn't support the screen recorded files, so I can't compile my singing battle into one video and I don't know what to do