How to add an existing system to a new account?

I had a system setup by Positronic years ago & they added it to pvoutput for me.

I then completely forgot about it for years, and am trying to setup an account etc. They gave me the number of the system and I can view it’s output without the account, I was just trying to add it to my pvoutput account.

Is this possible?

It is possible but will break existing logging (the API key will change) when transferring a system between accounts - https://pvoutput.org/help.html#general-transfers

So does that mean the system won’t log to pvoutput anymore? How would I re-set it up?

Only if you have access to the data logger and able to update the API key which will be different on your new account.