Inspect the back of the gauge. You should find a couple of screws that once backed out, will allow the gauge hosing to become loose. Prior to this, pry the gauge cover off. Now there should be access to the faceplate behind the needle pointer. Determine if the faceplate is bent towards the pointer locking it in place. If so, use a needle nose pliers to straighten the plate freeing the pointer and then re***emble.
If this is not the issue then heed Pscychodad,s recommendation on
replacement gauge.