Step 1:

Log in to your KAS (Technical Administration) panel using your credentials.

Click the menu item Domain or Subdomain, depending on where WordPress is installed.

Step 2:

In the domain or subdomain overview, please click the Edit icon right next to the respective domain or subdomain.

Step 3:

Now click on Edit next to SSL Protection.

Step 4:

On the Overview tab you can find the option Force SSL. Please switch it to yes and click the Save button afterwards.