Add the animation to a new track above your footage and set the composite mode to Overlay or use the 3D Keyer in the Color tab to remove backgrounds.

This guide explains how to download, customise, and use clean YouTube subscribe button animations for your videos. 1. Find and Download Animation Files

You can find professional, "clean" subscribe animations on several free platforms:

Import the animation via "Media" and use the Green/Blue Screen option from the overlay settings to make the background transparent.