Roof Rail Weatherstripping Tips On Install

Are you talking about the sealer in the roof gutter? If so, in the cases where it is hard and has cracks, I have used a flat screwdriver and a hammer and chiseled it out with the blade laid pretty flat to the gutter. It pops out in chunks. If it is tough, then I have used an angle grinder with a knotted wire wheel. Actually even if you use the screwdriver to remove chunks, the wire wheel will do a great job to clean it up.
Again, I'm hoping I'm talking about what you are asking for but to reapply, the sealer I have used came in a caulk tube and I simply applied it with a caulk gun, then with a nitrile glove on my hand, I either dip my finger in water or mist the sealer with a spray bottle so it doesn't stick to my finger and I trowel it out. Hope this is what you are asking for.