your dentist will have some tools either to wiggle the bridge out if it is loose or to cut it off in few areas and take it off the teeth.
At that point the abutment teeth will need to be examined. If restorable , and the gum and bone surrounding these teeth are healthy, then your dentist will remove the decay , and make a new dental bridge.
If one or both of the abutment teeth need to be extracted , then you have to discuss options of replacing the missing teeth with dental implants / longer bridge/ or a partial denture.
Each option has pros / and cons which you will need to discuss with your dentist.
The sooner the bridge is removed, the sooner the abutment teeth could be evaluated/ saved before the situation worsens. ....