Hi,
There is a few ways to create new or extend a tour
1. If this is just an extension of your existing tour ie: Sunset Cruise (Wednesday to Saturday) SUMMER
You can update the date restrictions to now include Sunday:
Then in your daily rates, you will be able to stop sell all Sundays excluding January.
You will then need to update the tour name" Sunset Cruise (Wednesday to Saturday) SUMMER "
Alternately, you can copy and create a new tour just for sundays:
Then complete the process above.