Dip your paint brush into the sealant enough to get a small drip or at least a full brush.
Drag the brush across the lips or eye without actually touching the paint so as to create a sort of small droplet of paint covering the area you wish to seal.
Leave it to dry for half a day making sure that the drip won’t slide down taking the paint with it.
Gently wipe/scrape off any excess by using either a q-tip cotton bud dipped in alcohol and then dabbed to remove excess liquid (because that would mess up your paint) or by using a toothpick.