Pretty simple. Go to a gif website and rightclick on the gif you want. save it to ur files then upload it to ur pfp.
How do you get a GIF as a profile?

To set a GIF as your profile picture on Chess.com, you need to upload the GIF file through your profile settings. Chess.com supports animated GIFs for profile pictures.
Here's how to do it:
Navigate to your profile settings: On Chess.com, go to your profile settings.
Find the profile picture section: Locate the area where you can change your avatar.
Upload the GIF: Select the GIF file from your computer.
Confirm and save: Click the save or update button to apply the changes.
Make sure the GIF file is a common image format like .jpeg, .png, or .bmp, and ensure it's at least 175x175 pixels
How???