The following article will assist you in changing the password of the MSSQL Server user 'sa' from the Plesk Panel.
Step 1: Log in to the Plesk panel with the Admin user.
Step 2: Click on the Tools & Settings page, then select Database servers.

Step 3: Here, you will see a list of installed database servers. Click on the HostName for MS SQL Server.

Step 4: Enter the New Password, and click OK.
