would like to change the minimum stay from 2 night to 5 nights

You can do this using the Rates, Calendar, use List view and open up on left hand side.  You should then see a Minimum stay line and you can do a bulk edit to change this.  If you can't see the Minimum stay line contact the booking.com help team using the Inbox icon on Extranet.

Hi Betty's Beach Condominium

How-To Setting minimum stay and context

Kind Regards

Contact BdC Support Team Options: 

For non partners/ not activated : https://partner.booking.com/en-gb/help/support-contact/how-do-i-contact…

For partners with full Extranet access - Extranet - Location of Partner Only Phone number and Message methods