The difficult I do immediately, the impossible takes a little bit longer.

Public Function IDOccurs(strTable As String, lngID As Long) As Integer
On Error GoTo ErrHandler
'From http://www.access-diva.com/

     Dim rst As DAO.Recordset
     Dim db As DAO.Database
     Dim myQuery As String

          myQuery = "SELECT * FROM " & strTable & " WHERE YourTableID = " & lngID & ";"

     Set db = CurrentDb()
     Set rst = db.OpenRecordset(myQuery, dbOpenSnapshot)

          rst.MoveFirst
          rst.MoveLast

     IDOccurs = rst.RecordCount

Complete:
     Set rst = Nothing
     db.Close
     Set db = Nothing
  Exit Function

ErrHandler:
     MsgBox ("Error:" & Err.Description)
     IDOccurs = True
     Resume Complete

End Function

Check for Duplicate Values...

Public Function IDOccurrences(strTable As String, strField, strID As String) As Integer
On Error GoTo Errhandler
'From
http://www.access-diva.com/

     Dim rst As DAO.Recordset
     Dim db As DAO.Database
     Dim myQuery As String

          myQuery = "SELECT * FROM " & strTable & " WHERE " & strField & " = '" & strID & "';"

     Set db = CurrentDb()
     Set rst = db.OpenRecordset(myQuery, dbOpenSnapshot)

         rst.MoveLast
         rst.MoveFirst
     
     IDOccurrences = rst.RecordCount

Complete:
     Set rst = Nothing
     db.Close
     Set db = Nothing
  Exit Function

ErrHandler:
     MsgBox ("Error:" & Err.Description)
     IDOccurrences = True
     Resume Complete

End Function

VBA
Place the below in your modUtilities or in a new Module, remembering not to name the Module the same as the Function, and save.  For more uses for this Function see My Blog.
For Numeric Data Types...
For String Data Types...
If IDOccurs("tblYourTable", Me.txtID.Text) > 0 blah, blah, blah...
If IDOccurrences("tblYourTable", "ytYourFieldName", Me.txtYourField) = 1 blah, blah, blah...
Use in an *If Statement* like...
Use in an *If Statement* like...
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