I'm trying to make one change to an AI file.

Erika,

All of the following is presuming vector artwork rather than a raster image.

If you have the text as live Type, you can just replace the second 1 with 2 and move the text to fit with its new width.

If your text is outlined, and if you have the font or can get it, you can lock the outlined 11U and write 12U, then place the new 12U with the outlined 11U as guide.

With regard to finding the font, you can try  the Adobe Fonts site (upload an image, clicking to the right in the search box, to find the same or similar) and have immediate access to your find(s),

https://fonts.adobe.com/

or you can use Photoshop to find the same or similar Adobe Font as described here,
https://helpx.adobe.com/in/photoshop/how-to/match-font-image.html

or you can try font finder sites such as the following (undoubtedly there are countless others),

https://www.whatfontis.com/
http://www.identifont.com/
https://new.myfonts.com/WhatTheFont/
https://www.fontsquirrel.com/matcherator

http://www.bowfinprintworks.com/ScriptIDGuide.html (Script fonts)

or hope that someone here knows it.

If, as I fear, your text is outlined, and you neither have nor can get the font, you can replace the second number 1 in 11U by a copy of one of the numbers 2 from 2024, with adjustments in width and position and rotation of the copy 2, which requires some intricate steps depending on the desired accuracy.