I hope you help me for making a unique ID equal 5 numbers with one later to be 6,
For Example 00125A
It is easy in Excel sheet as in the image1
“in excel sheet =TEXT(A2,“00000”)&B2”.

But in CommCare I find more changes, so please how I can make a unique ID when I enter (125) it gives me (00125) with the later(multiple choice) to be (00125A).

I’m not aware of a way to directly pad a number with zeros, but you can make it work with some creativity. This should do what you want for any number between 1 and 99,999:

My apologies - that approach won’t work. Any number below 100 will be converted to scientific notation, so you’d have to make a special case to handle that. Additionally, this approach will strip any trailing zeros. A much simpler approach would be to add 100,000 to your number, then use the substr approach above to drop the leading 1:

I think an easy way to do so is to register a phone number instead of integer for the digit part of the id, then concat with the letter…
Phone number question type register all numbers, even 0. The concat function automatically convert numbers into strings.