Dim iMax as Long
Dim iMin as Long
Dim MyNum as Long
Randomize(Timer)
iMax=99999
iMin = 10000
MyNum = Int((iMax - iMin + 1) * Rnd + iMin)
I'm not sure if your 1st digit is part of the 5 numbers or in addition to it.
If its in addition, then you can just use cstr to convert to a string and add it to the beginning or increase your imax and imin by one 9 and 0 and use the exmaple below.
If your field digit is part of the 5 digits then try
'Assumes MyDigit is your field value
Dim iMax as Long
Dim iMin as Long
Dim MyNum as Long
Randomize(Timer)
iMax=Clng(MyDigit & "99999")
iMin = Clng(MyDigit & "00000")
MyNum = Int((iMax - iMin + 1) * Rnd + iMin)