There is a very simple protocol mentioned in the following link which has worked for me. https://www.sciencedirect.com/science/article/abs/pii/0003269780900135
You should be aware that although some proteins will renature well after PAGE, other proteins are much more problematic to denature. It is very much a case by case situation and I do not know whether Cas13 will renature readily or not. This is presuming you want active protein. If you only need the denatured peptide then any of the procedures should be fine.