He sent you
his moveable.sed, which is completely useless to you. You will need to obtain
your moveable.sed using Seedminer, and the first step is for
him to run seedstarter.3dsx. Instructions are available at
https://github.com/narukaioh/pkm , though you'll want to use the main fork of Seedminer available at
https://github.com/zoogie/seedminer/releases .
You will need a PC with powerful GPU hardware in order to run Seedminer. My hardware probably can't do it. If your PC hardware is inadequate, you can try the Nintendo Homebrew Discord, or there might be someone here who can help you.