I stop working on the task and do something else:

– read,
– listen to music,
– watch certain movies (connected to the story because MCs like them, or they fit the overall theme),
– go for a walk,
– take a nap,
– take a bath,
– un-/load the dishwasher,
– cook / bake (grocery shopping)
– go to sport,
etc.

It's no use brooding over something when you're stuck.