Hi
If you are concerned that damage to your Apple Watch may be affecting sensor performance, then I suggest that you arrange for your watch to be checked by contacting Apple Support (mail-in service may be available, if required), making a Genius Bar reservation or visiting an Apple Authorised Service Provider:
Apple Watch Service Answer Center - Apple Support
Keep in mind that Apple advises that, even under ideal conditions, Apple Watch may not be able to record a reliable heart rate reading every time for everybody.
For the best performance from the heart rate sensor during workouts, ensure that you wear your watch snugly on the top of your wrist. Apple suggests that you consider tightening the band before starting a workout and loosening it again afterwards.
The sensor is likely to give better results for workouts that involve rhythmic (eg running) rather than irregular (eg boxing) movements. Other issues that can impact sensor performance include skin perfusion and wrist tattoos:
Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support
If your workouts involve flexing your wrists (such as when lifting weights, for example), it may help to move your watch a little higher up your arm, away from the flexing joint.
If you continue to experience issues with recording your heart rate during workouts, then, for more consistent readings, you may wish to consider pairing an external heart rate monitor / Bluetooth chest strap to your watch:
Use Bluetooth accessories with your Apple Watch - Apple Support
