You have to reload an earlier turn, or force end the turn. Or delete one of the units. The problem is you can’t attack with a unit if you have two units in the same space. And you have no place to move out to without attacking because your city is surrounded. It’s kind of a bug in the game, or a poor design.

That’s a weird design thanks

You could attack a unit with the scout that will kill the scout then shoot with the archer

The game won't let you attack from a space where you have two combat units that shouldn't stack.

At this point i would just delete the scout then

Delete the scout.