I have a little back pain, could you please softly thump me on the back?

(traditional) 我 有點 背痛， 你 可不可以 (輕輕的) 幫我 捶捶背？

(simplified)  我 有点 背痛， 你 可不可以 (轻轻的) 帮我 捶捶背？

*

pain    疼痛

could you please 你可不可以...?，你能...?

gently  輕輕//轻轻