Unable to continue a game with an anonymous player

Hi,

I have the issue, that I started a game with my father, sending him a link for the game.
We did several turns, but after some time he was no longer able to make moves.
The game seems to have forgotten that he is my opponent. (Session destroyed?)
Is there a way to renew the game, or make an account for him to transfer the started game to that?

Thanks

You can play from position, thus continue the game in that manner.