I think that very much depends. You need to make a judgement call ( or get a reliable reader to do it for you) on whether you've really overwritten or if there's enough plot to sustain two books.
Take an honest appraisal of your book. Is there a lot of unnecessary description that goes on for pages? Are there pages of back story that could be woven into the text or cut entirely? These may be indicators you could cut - a lot.
Or you may have a driving, exciting, suspenseful story that just needs to be two.
If it's the latter, though, you may need to restructure to make them work as a duology.
Good luck with it 🙂