Shoulder and back of neck pain

It may be a chronic disease of modern people, but I will ask.

My husband, who works in an office job, gained a lot of weight after getting married, especially around the back of his neck where the fat has become quite thick. When you touch it, the fat feels firm. His face is small, and his arms and legs are thin, so he looks slim to others, but he has a lot of belly fat.

Shoulder pain is severe, possibly due to the muscles behind the neck.

Even if I receive manual therapy, it only lasts for that moment... What kind of treatment would be good to try?