If you are going to replace the screw then why take off the washer? Or has the thread gone?.
Why not go out and buy a small pack of screws and washers the same size?
You could try leaving it in boiling water in a cup then pour into a strainer, recover the screw and see if the washer has loosened.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix general d.i.y.