We recently signed up for ATT wireless with HBO Max.
All worked well for 1 month, then unable to stream on any devices.
I'm now able to stream on phones and an Amazon TV after adding a new customer ID.
Although I can delete the HBO max app on my TCL TV, I can't remove the old account, can't enter a new customer ID.
I've spoken with customer service at ATT and HBO.
They were unable to delete, suggested I contact ROKU.
The TCL is our main TV, hoping for some ideas.
I don't have HBO Max so I can't give details instructions, but this is how it would work for the ones I am familiar with.
I'd expect there is somewhere in there where you can log out or disconnect from the account. Look under something called "profile", "options", "account" or something similar.
Once logged out you would then need to log back in, just as you did when you first installed the app, only this time, log into the new account.
Also, when you remove HBO Max make sure you restart your TV before adding it back. You can restart from the Settings menu or just unplug the power for several seconds and plug it back in.