How do you help someone with a trapped sciatica nerve?

Multiple ways: The sciatic nerve can be irritated because of a herniated disc, arthritis that results in tightening of the spinal canal, falls, injuries, or other rare reasons (tumors, infections, etc). Anti-inflammatory medications, steroids, physical therapy (especially with traction) can be helpful to relieve sciatic pain. If these treatments aren't helpful, surgery may be indicated.

Diagnosis: Find the nerve pinch and rlieeve the pressure.

Core Exercises: Typically core strengthening exercises are the best to help relieve pressure and forces in the spine. I would try and google some or look them up on youtube to see descriptions. If you can do them yourself, wonderful otherwise ask your doctor to get a referral to a good physical therapist for further assistance.