Log in to your Parallels account and go to the Subscriptions and Licenses > Register a License Key.
If you already purchased a subscription or license, enter your Parallels license key or a Parallels Access voucher and click Register.
If you don't have a subscription yet, you can purchase one from the Dashboard. Switch to this tab, scroll down to Available for Purchase, and click on Buy new subscription next to the product you'd like to purchase. Then select the product service plan you want.
Keep in mind that Parallels Desktop subscriptions include Parallels Access free of charge.
If you just want Parallels Access and don't need a Parallels Desktop license, choose Parallels Access.
Note: If you already have a Parallels Access subscription registered in your account, whether it's a stand-alone subscription or the subscription that accompanies a Parallels Desktop subscription, the Parallels Access item might not be available to you.