If I put another PlayStation network account on an old account. Will all my data stay from the old one?

I'm logging into an old account (not touched for 5+ years) and it's saying the PSN login is required but I've since lost the email. If I quickly boot up a new PSN account and log in, will I lose the profiles and accounts of my old games? In this case, I'm trying to log into his old fortnite account. Will it still be his old account or will it be blank with the new login?