A seat belt in a modern car is a one-time device in the same way an airbag is. Once it has restrained someone in a collision, it is finished.
Most cars fire a pretensioner that pulls the slack out of the belt in the first fraction of a second, then a load limiter lets it pay out under control so the belt does not injure the person it is holding. Both are consumed in the process. A retractor that will not pull out afterwards has locked for exactly that reason.
A used pretensioner cannot be recharged, and webbing that has been through a load limiter has stretched. It may still latch and still look normal, which is the dangerous part. It will not perform the same way a second time.
Belts, pretensioners and airbags are one restraint system controlled by one module. They are inspected together after a collision, because replacing one and leaving another is how a car leaves a shop looking repaired and is not.
If it has been hit and it also needs mechanical work, it does not need to go anywhere else.