A narrow gap where a kitchen backsplash meets the countertop can collect water and crumbs. Resealing a small, stable joint works best when the old material is removed cleanly and the new bead is compatible with both surfaces.
Check the cause
Look for movement, swollen countertop material, loose tiles, or water damage before applying new sealant. A flexible joint that has simply dried out is a reasonable small repair. If the backsplash is pulling away or the wall is damp, correct that problem first.
Remove and clean
Cut away loose sealant with a plastic scraper or a tool used carefully along the joint. Vacuum crumbs and wipe the surfaces with the cleaner recommended for the countertop and tile. Allow the joint to dry completely; sealant will not bond reliably to a damp, greasy surface.
Apply a controlled bead
Use a kitchen-and-bath sealant suited to the materials. Apply a continuous, modest bead rather than filling the joint with excess product. Smooth it with a damp tool or gloved finger according to the label, then remove masking tape before the surface skins over.
Cure and maintain
Keep the area dry for the stated curing period. Wipe spills rather than letting water sit at the joint. Reinspect after a week and whenever the counter moves. Persistent separation or staining behind the backsplash needs a proper moisture assessment.