I want to sell my sailfish x, do i have to unregister it with jolla or what?

i am already using a new phone. sailfish x is just sitting in my dress. is it like iphone? where you have to remove the device from your account.

You cannot do that to your Jolla account, I mean not even technically. It only lists the phones registered. You do need help from Jolla side. You can of course delete your account, but I do not know whether this action clears their databases holding the IMEI-account tuple.

The SailfishX License is tied to your Jolla-Account from which it was bought, Furthermore on first installing/activating it, the License will also be bound to the IMEI of the SailfishX device.

So as the others said, you will need to contact Jollas Zendesk Support to change this.

Depending on what you want to do they'll have to unbind the license from the Phones IMEI (if you just want to sell the phone and keep the License) or they'll have to Unbind it from the Phone and transfer it to the Jolla-account of the new Owner (if you also want to sell the License itself).