If laser weapons are put into actual combat in the future, and a person is shot by a laser, how do field medics provide first aid?

Treat it as a radiation burn. And there are hospitals that have treated people with laser pointers in their eyes.

But if it's a weapons-grade laser, you have to be careful about internal bleeding (although the area around the incision is definitely burned, the inside isn't guaranteed), and you have to be careful about secondary trauma from separating the burned skin from the clothing. Since they are all essentially burns, the treatment is much the same