Sel-catering - Restricting arrival and departure days

Can anyone help?

We are trying to restrict bookings to Friday changeover 7-night stays. I've tried following the advice at

https://partner.booking.com/en-gb/help/rates-availability/room-settings…

However If I attempt a trial booking through Booking.com the system allows changeovers on otdher days but Fridays.  I've noticed that my the options in the right hand panel inmonthly view on my page differ slightly from those described on the above help page, eg no 'advanced restrictions', only 'restrictions'.

Can anyone suggest a simple way to do what I want?

any help much appreciated

John