Enabling HTTPS redirection via the .htaccess file (Any Plesk version for Linux)
Note: This solution is applicable only if website is processed by Apache. In Plesk, go to Domains > example.com > File Manager. Open the .htaccess file, if available, or create a new one: click > Create File > type .htaccessin the File Name field > click OK. Once created, click on the file and paste the following content: Click OK.