Runner here.....had this happen to me before. Stretching helps; rolling a tennis ball on the bottom of the foot helps; rolling the foot on a frozen water bottle helps; wearing shoes with good supports (or inserts) helps. Try them all because not one thing works for everyone and you may need a combination of the two.

What worked for me was long, static stretches of the foot using a stair. I do these every day and especially before I go for a walk/run (using the curb). Stand on a stair with both feet. Take the toes of ONE foot to the edge of the stair and lower your heel to about a 45 degree angle....hold for 30 seconds. Repeat with other foot. Do this many times a day. It will hurt like the dickens but tendons need long holds to release the tension. If possible, build up to hold for a minute for each foot.

Alternatively, you can sit on the floor and stretch both feet using a towel. This is not as effective as your body weight provides more resistance than using your arms but it is a decent alternative.