I agree with Mike, you need to rethink the table design and normalize it. That means that rather than the lovely column layout, you will have a list with each set of credentials on a separate row. But to make the form work:
1. Add an unbound control to the form's header. As the rowSource, create a query that selects Jaar from the table and group by it. That presents a list of the years.
2. Add a where clause to your form's RecordSource query. Where Jaar = Forms!FABOS!cboSearchJaar
3. In the Click event of the combo add a requery --- Me.Requery