If you have purchased a Plesk license from one of Plesk partners, technical support should be provided by them. Plesk partners are fully trained and deliver best-in-the-industry support for Plesk products running on their infrastructure.
 

However, if you would like to get support directly from Plesk, you may purchase the Plesk support subscription.

Plesk support subscription terms

Support subscription purchase is available for two Plesk Obsidian latest releases only, please refer to Change Log for Plesk Obsidian.

Subscription has a free trial period for 1 month. If you order Plesk support subscription for a license for the first time, then you will be charged $0 for the first month and $10 for each next month.