Solved!
When you log in to Intervat, you can choose from various menus relating to vAT returns. I would like to submit an exceptional vAT return, as I received invoices on reverse charge VAT and I am exempted from VAT myself. Do you then also select ‘periodic return’? I am unable to click on ‘special return form 629’. It is not stated in the list. Thank you in advance for having answered my question! Kind regards, Bieke