Verb
(transitive, graphical user interface) To unselect (an item) by clicking.
(transitive) To undo or release a mechanism that clicks into place.
to unclick a seatbelt
Expecting a straightforward download I didn’t unclick what I should have and wasted 45 minutes cleaning the crap that was installed inadvertently. Source: Internet
When you sign up for a subscription be aware they automatically renew you and you need to unclick this button on your 'manage subscriptions' page. Source: Internet