If we have an SSL certificate with another provider, and they have given us the different parts of the certificate (KEY, CRT, CA), we can install it directly from Plesk. To do this, we enter Plesk > Subscriptions and click on the subscription we want to access.

Then, we go to the option SSL/TLS Certificates. Inside, we click on the button Add SSL/TLS Certificate.

Within this option, we put a name for our SSL certificate in the Certificate name option. Then we go to the Upload the certificate as text section. Here we copy and paste the different parts of the certificate (KEY, CRT, and CA). When we have done this, we click on the Upload Certificate button at the bottom.