This lib can't parse aseprite's animation config files, it has it's own. Docs are here: JSON configuration · Whitebrim/AnimatedSprite Wiki · GitHub
Main difference is that animation is based on playdate's update frames, not time in ms (like in aseprite)
For example if your game is targeting 30 frames per second, then each frame will take 33ms to draw. If you want to convert 100ms animation into frame animation, then you need to set tickStep to 3 (3*33.3ms=100ms).
Basically you need to write new config file based on your aseprite configuration. Please write what animation settings and states do you have and I'll create config.json for you as a little demo. The only problem that might occur is that AnimatedSprite lib currently don't support different animation speed for single state: the workaround is to use different states.