Turn off power at the breaker
Verify power is off with a tester
Remove the switch plate and pull out the switch
Identify the common terminal on each three-way switch
Connect the incoming hot wire to the common terminal on the first switch
Connect the switched leg to the common terminal on the second switch
Connect the two traveler wires between the traveler terminals on both switches
Connect the ground wire to the green ground screw on each switch
Connect the neutral wires together if present in the box
Secure all wire connections with wire nuts
Carefully tuck the wires back into the box
Mount the switches back into the electrical boxes
Reinstall the switch plates
Restore power at the breaker
Test the light from both switches