Hi BRYAN HERRON
Just to double-check, the user will input the digits in an integer question, is that right? The format you're after would need to be stored in a text question to accommodate the plus sign. One way to achieve this could be to use a combination of the string-length() and substr() functions, as described here: Formulas—Survey123 for ArcGIS | Documentation
A calculation for the text question could look something like the below (given an input in an integer question called "int1"), but you would need to test this to make sure it works for your application. The calculation below should work for three-digit numbers and greater; you could then incorporate it into a nested if() statement to cover the one- and two-digit cases.
concat(substr(${int1},0,string-length(${int1})-2),'+',substr(${int1},string-length(${int1})-2,string-length(${int1})))
Hope this helps,
Cheers,
Jim