You might try updating via the djigo4 app installed on the Pro + model monitor. Turn on the wifi of the monitor and connect, it should immediately see any available upgrades.
If you happen to have a P4 Pro Plus vr 2.0 you need a different version of the assistant. Called DJI Assistant for Phantom. You did not mention a vr 2.0, just wanted to add this to make sure.
Paul C