Copying ssl certificate from one server to another in plesk

> Have an odd situation where two servers sit behind a load balancer and only one can renew its ssl certificates with lets encrypt. So I copy the certificate from one server to the other. Plesk is unhelpful for this because the certificates page only allows upload of a .crt file but the gives you a .pem file when you click download.
The bit I have to remember is that you can upload the pem file you downloaded but you have to go to Websites and Domains > domain name > SSL/TLS Certificates and click unassign on the existing certificate first. Then you get the option to upload the pem file you downloaded from the other server.
Hopefully in a couple of months time I will remember this when it happens again.