This is called the back buddy, and can be useful in getting pressure on knots the are hard to reach with your hands!
Body Back Buddy Back Massager with Poster (Purple) | Handheld Massage Stick | Trigger Point Massager https://www.amazon.com/dp/B07664ZWSP/ref=cm_sw_r_cp_api_i_6R9oDb7FKRJSG