Hold for 20-30 seconds with the knee straight and with the knee bent to target the whole calf muscle complex. Repeat both for 3 rounds, twice per day.

In most cases, stretching the achilles while under tension can worsen symptoms early on. This is why I recommend doing this exercise on flat ground first.

Addressing all possible contributing factors (shoes, strength, ROM, muscle tension, running form etc) is key for a full recovery, but this exercise can get you moving in the right direction.