Turn off power at the breaker
Verify the circuit is de-energized with a voltage tester
Identify the two 3-way switches and the 4-way switch location
Run a 3-wire cable between the first 3-way switch and the 4-way switch
Run a 3-wire cable between the 4-way switch and the second 3-way switch
Connect the incoming hot wire to the common terminal of the first 3-way switch
Connect the two traveler wires from the first 3-way switch to one pair of terminals on the 4-way switch
Connect the two traveler wires from the other side of the 4-way switch to the traveler terminals on the second 3-way switch
Connect the common terminal of the second 3-way switch to the light fixture hot wire
Connect all neutral wires together in the electrical box
Connect all ground wires together and to each switch ground terminal
Ensure the 4-way switch is wired with matching traveler pairs on each side
Secure all wire connections with wire nuts
Mount the switches into the boxes
Install the cover plates
Restore power at the breaker
Test the light from all switch locations