Adding old dough to a croissant recipe

hi guys, so I already have my go to croissant recipe, which I will post, however  I would like to add 18% of old croissant scraps for more flavor, but I do not know how to incorporate it and how much  to add . Can you please help me to figure out the amount in grams needed. Here is my recipe:

800 gram flour 

520 gram milk 

100 gram sugar 

5 tsp yeast

4 tsp salt

55 grams butter 

total dough : 1.5 kg