No idea on what they use for your machine, but most filter type pressure switches that "lock on" once activated, have a little button on the side of them to push and reset. If it is not on when idling and comes on with load/revs you still have a problem, or one of the hoses to the switch has fallen off if it's an externally mounted/piped one.
If the tractor has a computerized dash, check your user manual as it's probably just a preset number of hours that also brings it on, to get you to clean the filters and needs to be reset via the dash selection.