How do I change date and time on photos on IOS?
You can do this photo at a time by first downloading the Exif Metadata app. Once this app is installed, open it and allow it to access your photos. Select a photo and then near the bottom of the screen, you'll see EXIF followed by metadata. Scroll all the way to the bottom and you should see an Edit Exif button. Press this button and press on the date of the image. it should be the 1st displayed line. You'll be able to change the date.

The app is free from the app store. it has an in-app purchase for the pro version.  The pro version claims you can do multiple files at once. I haven't figured out how.

If you have a Mac computer there is a way to change the date on all at once. Just let me know, in the comments, if you need this.