Adding new national teams and their players


Club Supporter
Hello, I want to try to recreate all FIFA-member national teams in FIFA 21 (21 cause I don't plan to buy FIFA 22) and playing national teams matches is the only thing I want to do right now. Is there anyone who can help or explain precisely (step by step the best) how to add new national teams (best) or change existing teams names, logos and players to recreate nationals. I would be very grateful for explaining me how to do it.
If it would look sensible I would very willingly share my work.