You have the right idea - find a good Sports Rehab doctor and follow their advice.
Working with a therapist can also help guide therapy.
Still, understanding the basics in return to play should help.
As you have already done, rest is the first step until almost all the pain is gone.
A common first step is to do very gentle "range of motion" exercises.
These are not to truly "strengthen" the muscles, but rather to get the muscles and tendons smoothly gliding past one another again.
[Some internal "scar" tissue may have "glued" adjacent tendons/muscles together. Loosening up some of this internal scar tissue may cause some minor soreness, but should not cause real "pain".]
One of the most common range of motion exercises is to use the red Theraband Flexbar, doing the Tyler twist and reverse twist.
[The red Flexbar seems "too easy" to many, but again the objective is just to get the muscles and tendons moving past one another again.]
If there is no pain with the red Flexbar, it is then time to progress to the green Flexbar.
Slowly increasing the number of reps can let you begin to increase some strength without overdoing it.
Any return or increase in pain means you need to drop back a step and start over after the pain is better.
Next, strengthening the forearm even more with other adjuncts, including dumbell wrist curls, reverse curls and pronation/supination exercises can build more strength.
Return to tennis should be gradual - start with short hitting sessions without serving.