Converting it

Use an online convertor (search up .ani to .gif) and download the gif. Cut some frames from the .gif file if it has more than 25 frames.

Stacking

Convert the gif into a sprite sheet here. Click "Stack vertically" Change the "Margin around tiles" to a good enough number (10 is usually good) Covert and use the save button to download the png.

Putting it in

Drag the png file into mousecape. Change the frame number to the number of frames the png has (how many individual images are on the png?) Done