if you want to consolidate both servers on to one raspberry pi then that’s not a problem
move the web server configs etc to a raspberry pi
then run the -expand flag and add the domain for the domain you transferred over.
This will create a new certificate with the original domain and the new domain.
But it does have the advantage that your certificate chain is updated
Have a look at -expand here: Reverse Engineering Certbot Expand Option to Use with Another Client
Andrei