I don't understand what you mean that something doesn't work. If you bought your license through Plesk directly, you can simply go to
https://support.plesk.com/hc/en-us/requests/new to open a new request entering in your PLSK key to open a ticket with Plesk. If you didn't bought your Plesk key from Plesk but from a third party reseller, go through the link Peter provided to purchase a support plan (you get 30 days for free so you can take advantage of that) to attach a support plan to your PLSK key then go to that support request page and submit a ticket.