Solution:

1. We can do that by integrating Helpdesk with Subscriptions and Website.

2. First make sure that your Recurring Plan period has the Self-Service checkboxes unchecked:

Note: On Odoo 16 it's going to be under Plans:

Note: On Odoo V15 it's going to be under Subscriptions Template:

3. Create a Helpdesk team and check the Website Form checkbox:

4. After you create the Subscription:

5. The Customer can go to the Website and submit a ticket:

6. The Helpdesk Team will receive the ticket:

7. The Team can then click on the Customer field and go, the Contacts model, go to the Subscription, and manage the Subscription: