The program files should be located around: ~/Users/[USERNAME]/Library/Application Support/Godot/app_userdata/PNGTuberPlus
Your saved avatar should be in that folder, and you can upload further images there to load them as new sprites. The esc key likely doesn't work on MacOS due to the way the program is coded, but so long as you have mouse input, because you can still click "Add Sprite" and achieve the same result.