"You have not provided enough info to get assistance. What kind of bow? Compound or recurve?" Good point, Cossack, too many "IF'S"

However, IF it's a compound, and IF it has solid limbs, and IF you could just reserve the string, you can make a gizmo like in pic and do it yourself. Kudos to Matthias 72 from the Italian site for the pic, btw.