Try something like;

Public Sub StrTest()
Dim Strng As String, aChr As String, i As Integer, FirstStr As Boolean
Dim str1 As String, str2 As String, str3 As String

Strng = "123XYZ24"

str1 = "": str2 = "": str3 = "": FirstStr = True
For i = 1 To Len(Strng)
aChr = Mid(Strng, i, 1)
If InStr("0123456789", aChr) > 0 Then
If FirstStr Then str1 = str1 & aChr Else str3 = str3 & aChr
Else
FirstStr = False
str2 = str2 & aChr
End If
Next i

Debug.Print Strng, str1, str2, str3

End Sub