First you need to install Python on your computer. Follow the instructions in this video: https://www.youtube.com/watch?v=tCYsBsN1RNg
After install, open the Command Prompt (cmd)
Type “py” or “python” and hopefully you will see some text showing you the current Python version installed. If not, you must add “path environment variables” as described in the video.
Once you successfully get version feedback from the “py” or “python” command, open a command prompt window in the folder where your glTF file is. See instructions in this video: https://www.youtube.com/watch?v=bgSSJQolR0E
Type "“gltf_merge_anim.py in.gltf out.gltf” (replace “in.gltf” with the name of your glTF-file)