Kitchen tiles were incompletely done. Help with a finish touch idea?

Can you include a picture, please? You'll receive better answers if you can show or describe how the tile is incomplete. Are the tiles grouted?

take a picture on your phone and take it to where ever you will be buying your tile from and show them, they will give you ideas and show you different options, hope this helps

The places where the tile meets the walls should be caulked. If the grout was not finished, you can mix more grout, spread over the tile to fill in gaps, packed and neatened with your finger or a work glove, then the tiles cleaned quickly with a damp, clean cloth. When the grout has cured about a day, you can go back over the tile with another damp, clean cloth. If the grout was not sealed, you can go over the tile and grout with 1-3 coats of polyurethane. If you want a nicer edge at the wall, you can nail or staple in quarter round trim, or taller trim on the wall and quarter round in front, similar to building crown molding on the top of a wall. All, I hope this address some of your questions. Best wishes ☺️

Now that I’ve seen the picture, I’m nearly horrified. The window is not square the shelf is not even with the wall, and instead of fitting and cutting the last row of tiles, the person just grouted in the space. Since the last row would have been crooked, then the first uneven row is probably the bottom one. I have one new solution for you. Buy or make a really wide wood frame for just inside the window and hang it straight. Paint it white, stain it, or paint it any shiny coordinating or contrasting color. Make sure it covers the grout and another row of tiles or more. The frame will distract most eyes from the tiles. I’m sorry ☺️