Used personal AppleID on business iPad. Now changing to new iPad and don't want to lose information

I have a few devices using my personal AppleID (iPhone, iPad, AppleTV).

When my company shipped me a business iPad a few years ago, I accidentally used my personal AppleID. I noticed my personal photos were showing up on my business iPad. I figured out how to keep photos from showing up on my business iPad, and so iCloud would not update my business iPad with them. I can't remember what I did, about a year ago to make this happen.

Now, I'm getting a new business iPad and want to switch to my business AppleID. I have a business iPhone that uses my business AppleID. However, I noticed on my current business iPad that my personal messages were also showing up on it. ALL OF THEM. I'm afraid to delete them, as I don't want them to get deleted on other devices....the same as is the case with my photos. What is the procedure for blowing away (completely resetting to scratch) my current business iPad. I have nothing on it that is not already on my business laptop or iPhone. I assume I detach from all networks, and then do something to reset the iPad. Just want to make sure it will never delete my messages, or anything else