ȷᥲᥴkіᥱ

step 1. - open your banner in photopea

step 2. - find whatever gif you want to use in your edit + download it

step 3. - click File > Open > then select whichever file is your gif

note; don't click "Open & Place," your gif won't work if you do

step 4. - if you did step 3 right, a new project should appear next to your banner [like in the pic below]. click on that

step 5. - now you're going to right click the folder containing your gif, and click "'Duplicate Into ..." For the destination, select the project containing your banner

step 6. - now that your gif is in your banner, you can mess with it just like an image. Just make sure that when exporting your banner, you export it as a gif