You need Manager user role to access this function
1. Go to 'Site Administration>Configuration'
2. Click 'Hotel interface'
3. Click 'Edit' at the end of the row
4. Find public last arrival date and intranet last arrival date setting.
5. Select if you want to use Absolute or Relative dates by checking the checkboxes
If you select absolute date enter a last day of booking on the format YYYY-MM-DD
If you select relative date enter a date on format "1y+1m+1" this example means that reservations can be made 1 year+ 1month+ 1 day ahead in time. In the image above it is set that hotel can book 36 months ahead while guests can book online and in booking channels 12 months ahead.
6. Click 'Save in top right corner to save your changes.