I've had quite some experience with this... tennis elbow then golfer's elbow in my right arm, then tennis elbow in my left arm, all over the course of 3 years. The YT therapy videos will certainly help, although you'll have to experiment to find ones that are effective.
The game changer for me was working with a Theraband therapy bar consistently. You basically twist it against resistance like revving a motorcycle. Comes in varying resistance strengths but I ended up going with the strongest one. The pain/discomfort level in using it is high at first, but if you use it consistently (I kept mine at my desk at work as a "fidget tool") it offers relieve short term and a strengthening of the forearm muscles to avoid tendonitis recurrence long term.
https://www.amazon.com/TheraBand-Ten...=operasport-20