How to create rename method for photos

We take photos of eyeglass repairs.

These photos are located in large folders (up to 10000 pictures) sorted by date.

The first photo is the order number for that repair. It is a picture of a black background with numbers. Then follow 10-25 pictures of that repair.
Then comes the next photo of the next order number, etc...

What would be the best quickest way - method - workflow to organize / rename these photos by order number?

At this point the photos are only named by the camera ( IMG_xxx.jpg)

Any help on this is greatly appreciated.

Thanks

Stefan