See How to create a new Apple ID https://support.apple.com/en-us/HT204316
Some of these things will apply to your situation even though you are not changing your Apple ID: What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071
Keep in mind that some things available under the first Apple ID will not be available under the new Apple ID. For example, you won’t be able to transfer anything purchased from the App and iTunes Stores to the new ID. And, there are other issues to be addressed. See
what Eric Root say on this matter here: https://discussions.apple.com/thread/251263630
what Winston Churchill says about it here: https://discussions.apple.com/thread/7452747