I would like to know how to stack multiple artboards to make one artboard.

Adobe Illustrator two artboards into one

I am using Adobe illustrator on Windows 10.

I was creating a poster,
I was working on an artboard with images and text on it, but before I knew it, the large image I had on artboard1 became the artboard2, and the text on it moved with the artboard2 created from that image.

Personally, I would like to change the artboard2 created from this large image back to the original large image.

I would also like to know how to stack multiple artboards to make one artboard.

Thank you in advance.