I've had elbow tendinitis off and on for 30 years. I triggered it most recently by doing too much heavy grip work (deadlifts, farmer's walk, rows, pull-ups). Once it flared, it became impossible to do any underhand movements (aka curls) or heavy grip work. It took half a year, but I knocked it down to nothing, while continuing to lift the entire time.
1. Completely stopped all underhanded movements (including curls); I could still do neutral grip movements, but didn't do hammer or overhand curls since these still aggravated things (just not as much as underhand).
2. Bought Nordic Lifting elbow sleeves, and put them on 30+ minutes before every workout (incl. legs).
3. Bought Versa Grip Pro grips, and used them for every single pulling movement (rows, cable work, deadlifts, ...).
4. Bought DashSport counterforce straps for both forearms. Wore one set during every workout (incl legs), and another set for daily use. They stopped making the exact ones I got, but there are other ones with a similar design (needs the gel pad to press down on top half of forearm).
#1 to #3 halted the flare up and slowly let it recover. I didn't do #4 until months later, and within days it completely knocked down what was left of my flare up. I can't describe how impressed I was by the straps. When I feel a flare up start now, I put the strap on and it is gone in a day or two.