google it

Here is a link that might be useful: how to patch a small hole in drywall

I'm hoping a smaller application tool for grout lines this size is available. That's the main issue.

Cut 1/2 the bristles out of an old toothbrush and, voila, a grout sealer applicator!

Or use a foam brush - they are beveled.

Thank you, everyone, for your help. The beveled edge 2" foam brush worked best. It did get "mushy' the longer I worked with it which caused the sealer to spread onto the tile and have to be wiped off, so my "note to self" is to buy several and rotate through them next time I need to seal this grout. Done!!

Home Depot sells small plastic bottles with thin brushes on the cap just for applying tile sealer. I bought one and it worked great. The description says "for walls".. but it worked great on the floor.

Here is a link that might be useful: Grout Sealer Applicator Brush Bottle

I went to the hardware store and got a spray can of grout sealer. Just follow the directions.....to just spray the grout line and wipe off the tile with a dry cloth. Let dry overnight. So easy.