I have tried to anneal PETG and it just don’t worth it for my blend (devil design). It will become harder and brittle. I use annealing for Polymaker PCmax with great results. There are plently of articles for PLA crystallising with great results but it require oven with controller that support temp curves. It requires tem increase to 50 and than slowly and gradual increase in the temp up to 80C fir few hours.