To auto populate your text box with the next Id where Id contains alpha characters and numbers, It's gonna take you some coding. What you want to do is on Open Form event do the next.
Private Sub Form_Open(Cancel As Integer)
'This Function will auto populate text box with the next Id
'taking that Id contains of 4 characters
'(2 leading alpha characters + 2 trailing numeric characters).
'Note: It will only work if 2 leading alpha characters are in Upper Case.
Dim db As Database
Dim rs As Recordset
Dim sql As String
Set db = CurrentDb
'The below Select statement will return the Maximum Id value.
sql = "Select Max(Id) as MaxId From Table1"
Set rs = db.OpenRecordset(sql)
If IsNull(rs!MaxId) = False Then 'At least 1 Id already exists
With rs
If Mid(!MaxId, 3, (Len(!MaxId) - 2)) = 99 Then 'If 2 traling Numbers has
'reached 99
If Asc(Mid(!MaxId, 2, 1)) = 90 Then 'If second character equals "Z"
Text0 = Chr(Asc(Left(!MaxId, 1)) + 1) & "A" & "1" 'next character in
'alphabet + "A" + "1"
Else
Text0 = Left(!MaxId, 1) & Chr(Asc(Mid(!MaxId, 2, 1)) + 1) & "1" 'first character +
'next character in alphabet + "1"
End If
Else
Text0 = Left(!MaxId, 2) & Mid(!MaxId, 3, (Len(!MaxId) - 2)) + 1 'Max(Id) + 1
End If
End With
Else
Text0 = "AA1" 'Create first Id
End If
End Sub
I hope it works for you!