Achilles tendonitis came back. what can i do to treat and prevent it?

Eccentric stretches: Eccentric stretching and strengthening of the calf muscle and achilles' tendon has been shown to be most beneficial for recurring cases. An orthotic with a small heel lift may be useful for a year or so.

Recurrent tendonitis: In this case, you need to strengthen the tendon. I find prolotherapy works well to strengthen and repair the tendon.

Eccentric : Agree with above answer. Best treatment for prevention is eccentric strengthening exercises.

Stretch!: Make sure you do your warm-up and cool down stretches consistently. Check your shoes and make sure they are not wore out. Adding an arch support or heel pad may be beneficial. Temporarily hold back on your exercise intensity or duration.