Just so we get the field names right, what is the name of the field that contains the data "General 1", "A1", etc...?
OK, so the task is to change instances of "General 1", "General 2, "A1", A2", etc... into "_1", "_2", "A1", A2", etc...
You need to find out which of those begins with "General". For that, you need the Left() string function. This fornula: Left("General 1",7) results in "General". This formula:Left("A1",7) results in "A1". That's what the number 7 is used for.
Now that I've successfully found which of the data begins "General". But there are more than one type of entry that begins with "General". There's "General 1", "General 2", etc... We still want them to sort correctly. We need the number. That's where the Right() function comes in. This formula: Right("General 1",1) results in "1". That's where that number 1 comes in.
If you have "_" and you have "1" and you want to concatenate them to form "_1", then you use the ampersand operator like this: "_" & "1". That produces "_1".
We still need to handle the situation where you could have "General 10", General 11", because then we can no longer use Right([yourstring],1).