How so?

Yo dad, heres the login:
username: dad
password: Pa$$TheP0p

If it asks for a URL on the first screen input the following URL: https://jellyfin.domain.tld/

If you (or a relative) can’t manage that, I’d be afraid to even let you handle a car or open a bank account.
Can’t imagine you relative doesnt also have to create a plex account somewhere to then be invited to the plex share or input the URL to request access.