Remove the parameter from the query itself. Then when the form loads, ask the user via an input box what they want. Then set the form's record source via VBA code. View the query in SQL view to get the proper syntax for the VBA code, but replace the portion where you had the parameter with the proper input box answer.
strCustomerID = Trim(Nz(InputBox("Enter the Customer ID.", "ID?"), ""))
If Len(strCustomerID) = 0 Then
'Input box is empty. Select all records.
Me.RecordSource = "SELECT * FROM tblMyTable;"
'Input box is not empty. Select specific records.
Me.RecordSource = "SELECT * FROM tblMyTable " & _
"WHERE [strCustomerID] = '" & strCustomerID & "';"
I have not tested this.