Worn caulk along a sink backsplash can let water reach the wall or cabinet edge. Replacing it is mostly a preparation job: remove the failed bead, dry the joint, and apply a continuous bead that can move slightly as surfaces change.
Remove the old sealant
Cut both edges with a sharp utility knife and lift the old caulk carefully. Scrape residue without gouging the counter or backsplash. Vacuum crumbs and wipe the joint with a suitable cleaner.
Dry and tape the joint
Let the area dry completely. Apply painter’s tape on both sides of the joint, leaving a narrow, even gap for the new bead.
Apply and tool the bead
Use a kitchen-and-bath sealant compatible with the surfaces. Run a steady bead, then smooth it with a damp tool or gloved finger. Remove tape while the bead is still workable and let it cure as directed.
Protect the repair
Keep the sink edge dry during curing. Recheck after a few days for gaps, lifting, or water collecting behind the joint.