Rub backwards and forwards around the tendon (across it) gently with all your thumb or finger pads until the sensitivity fades, which must just take not more than a moment or two, then boost the intensity a bit and repeat. Rollers are available at most gyms (and never employed Substantially), https://www.theorthopaedicandpainpractice.com/why-do-my-outer-elbows-hurt/