Element Home App:
Tap the scene bubble that contains the bulb you wish to remove. Tap the three dots in the top right corner, then tap "Manage Bulbs." Then, tap the red trash can to the right of bulb you wish to remove from the scene. This bulb will now become an unassigned bulb.
Sengled Home App:
Tap the specific room in the room tab. Tap the specific bulb you wish to edit. In the upper right hand corner is a hexagon shape for the settings page of the bulb. Tap the room and select which room you would like to move the bulb to. If you want to add it to a new room, tap the + icon in the upper right hand corner to create a room.