Try to get it off. I always put the chick in my left hand with my hand over its top and wings with it's butt poking out between my thumb and forefinger. I hold it close to my tummy, that way the chick doesn't freak out. Seems to work pretty good.
then I get a bowl of warm water with a saturated paper towel and hold the towl against pasty for a minute or two, resaturating every few seconds. Pasties come right off even if they are dried.
I had a few with pasty butt the first couple of days.... what worked the best for me was cotton balls & Q-tips w/warm water. For some reason the cotton balls just worked better than anything else. If the PB was bad or really dry/hard I saturated it with the cotton ball, keeping the chick warm and secure in my hand. I used a dry cotton ball to dab-dry and when done put her back under the heat lamp.... worked for me!