well, my friend speedruned phasmophobia with me and we don't know how he can add me to list of players with that link to thier accounts

Whenever you submit a run to a multi-player category, in the submission form you will have textbox fields for each player: "Player 1", "Player 2", etc. Your name will automatically be on "Player 1" (can be changed with the "You are" dropdown list). You will have to manually write the usernames of the relevant other players in the other textboxes.

It should be noted that if you do not see a Player Two box on the submission form then the category/game does not support multiplayer runs and if someone assisted you with your run then it would be invalid. Runs are intended to be single player unless otherwise specified.