The screw that holds the Enviolo shift actuator assembly to the hub has likely come loose. Remove the rear wheel and retighten the screw. Make sure the actuator is clocked in the proper orientation on the hub. The screw is identifiable by its long screw driver slot. I would recommend removing the screw and applying a dab of blue Loctite to its threads. You will want to do this as soon as possible to avoid damaging the splines on the hub and actuator.