I'm a sports physio with an interest in tendons.
An individualised approach including some of the following normally gets these better.
- heel insert
- avoidance of stretching
- specific strength program (calf but often also further up the leg)
- close monitoring of run volume/speed/terrain (e.g. hills)
- addressing of other 'lifestyle' factors e.g. poor insulin sensitivity/blood sugar control / increased weight
there are other options that can be used in specific situations but are more invasive
- shockwave therapy (as mentioned above, good as an adjunct but not a sole treatment)
- high volume injections of saline +/- small amount of steroid into the tendon sheath (not the tendon itself)
- AVOID steroid and blood injections into the tendon. These are unhelpful at best and harmful at worst (and expensive)
If they are chronic, or there is severe limitation of function (e.g can't run at all), they can take several months (2-6) to get very good again. There's no recipe (unfortunately!) and often no 'quick fix' solution. Bike/swim are completely safe and unlimited in the meantime. Good luck!