I'm looking to insert a character at a specific place in lines of text. I played around with this in the summer and figured it out, but didn't take great notes and now I can't get back to where I was. I'm hoping someone can help me out here as it's a pretty simple query that I just can't seem to get, and I'd like to move forward with this part of my project.

There are 3 different permutations of text.

1 1/1 [letter] digit space digit forwardslash digit space letter
1/1 [letter] digit forwardslash digit space letter
1 [letter] digit space letter

I'm wanting to insert a character right before [letter].

Your help is appreciated, thank you!