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You need to save them on GIF format(on Photoshop), remember to save them through the legacy option (halo 0%, transparency depending on what you are doing) and in the top are 2 options, Original or Optimized, you can change that too.
Once you have your GIF file, you need to convert it to APNG, how do you do it? Through online apps, I recommend aconvert, good, easy, and works great with the FS system of avatars.