log into your Plex Pass 2 account with your web browser
accept the invitation from Plex Pass 1 account.
Log your client(s) into Plex Pass account 2
They can access libraries and servers of both accounts. But you can only schedule DVR recordings or change settings of servers belonging to account 2.
If you need to change settings on server belonging to account 1, you need to use the web browser and log into account 1 instead.
If you have ‘managed users’ on account 2, they cannot access the servers of account 1. Only the ‘main’ user of account 2 can do it.