Once you have created the CSR and receive the certificate from the issuing authority, take the following steps to install it to the hosting plan through Plesk Panel.
1. Log into myTophost Panel and click on Plesk Login in order to connect to the Plesk of the plan that you are interested in.
2. In the Websites & Domains tab, click on Show More.
3. Click on SSL Certificates.
4. Click on the name of the certificate.
5. Upload the Private keys, crt key, CA by clicking on Choose File on the right-hand side of each key.
Alternatively, you can copy paste the keys that you received in your email.
In the field Certificate (\*.crt), paste the first key that you received (main certificate) and in the field CA certificate (\*-ca.crt), paste the root and Intermediate (double key) one under the other with no blank line.
6. In the Websites & Domains tab, click on Hosting Settings.
7. Find the section called Security. You will see the option SSL Support being ON. Select your certificate from the drop down menu. Click on ΟΚ at the bottom of the page, in order to complete the process.
Related article: How can I install the SSL in Plesk for the webmail?