Put the bowl of the mixer and zero. Add the older dough and check the weight. You can add new bread flour, water and salt to about the same weight.
Add the flour and water in a proportion of 2 to 1. eg 400 g flour and 200 ml water and a tsp of salt
Mix with the stand mixer for about 8 minutes, starting slowly for 2 minutes and then speed up
Add a small amount of flour or water as required
This will be ready to bake tomorrow