You are in your position of your forward fold.
Take one leg and bend backwards at knee so that the heel of the foot sits beside your bottom.
Roll the calf muscle out the way it give you a bit more room and stops pinching.
Breath in and lift the chest and straighten the back.
As you breath out fold forwards leading with the chest.
Remember when you are as far as you can go relax the neck and look towards the knee.
I always find that I can get further down in this position.
Use a strap if you cannot reach your feet.