I had a metric boatload of coleus germinate and faced a similar thinning problem.

With the soil moist, but not-too-moist, I was able to identify the plants to keep, and pluck the ones "far enough" away right out of the dirt. Ones closer, I just snipped their tiny little heads off.

It's painful and difficult to pick a plant to live and a plant to die. But ultimately, it's for the best.

The remaining plants will say "thanks" and get all growy on you.

Good luck!

To pretty much echo what Bob said. I chop the extras (above the soil) with scissors.

Sometimes I'll attempt to dig up the whole bunch and gently separate them. But I do that knowing that I might end up with no seedlings.

Clipping away the extras (without disturbing the roots) is the best way to go if you want to increase your odds of ending up with a at least one strong seedling.

You can try to take this approach which is what I do to thin most everything I plant, but you might want to close your eyes while doing it. Take a small garden rake with a medium spread between the tines and gentley rake through the seedlings.It's fast and easy and will save you lots of time trying to thin them by hand. You'll be amazed with the results in the long run.I promise!!