Safely un stringing / stringing powerful Medieval replica crossbow

Hi ,  I wonder if any member could give me some advice on how to safely string and un string my 200 lb Medieval replica crossbow I've watched a number of tutorials on Youtube and un stringing it was not really a problem using a block of wood on the ground and applying pressure to one side of the prod , however trying to restring it was a real problem , it eventually took three strong men and a hook to eventually get the bow re strung ! Any advice would be gratefully received also if ...