What exactly is it doing when it "won't allow me"? Is it going into a corner and sulking? :-) Is there an error message and if so, what is it exactly?
When you say "new Apple ID" do you mean you set up a new account, or do you mean you changed the email address on an existing one and now want to change it back to the old address? If the latter, Apple does not have a statement about email address re-use in its documentation that I can find but here is an April 2021 post by ASC contributor IdrisSeabright that was recommended by the official Apple team -
"Once you've used an email address as an Apple ID, it can't be used again for an Apple ID, even if the first Apple ID has been deleted."
https://discussions.apple.com/thread/252629414?answerId=255095641022#255095641022
This is in accordance with what is claimed in this April 2021 post https://discussions.apple.com/thread/252629414
- Original post: "I tried contacting chat support and finally phone support today and they told me that you can NEVER use an email address that was used for a deleted account."