Is it a stress crack i.e. will it redevelop, or is it an impact crack? Is it a surface crack or does it go right through? Delamination can be felt by the area being abled to be pushed in to the surface behind.
For a minor surface or non stress crack there is a marine product called Creeping Crack Cure. Available in small squeeze bottle. One step. Ramping up the job a little, the next step would be carefully opening the crack just a little & using either straight resin or resin with fairing filler to fill the area, then wet sand & paint over the area.
A stress crack will need the surgery treatment with roughing up the whole area, patching with a couple layers of fine cloth, sanding, filling, sanding some more, fairing filler, sanding, primer, wet sanding, painting, compounding, repeat steps as necessary. You want to avoid that if you can. What looks like a little job becomes a ver labour intensive thing to make right.