Property change of use

I currently have a a commercial building split into 1 bed studio flats and I want to change its use to sui generis and run a hostel.

The local council advised I need to change the building use from its current set of flats to sui generis and apply to change the council tax from flats to one commercial dwelling.

I also need to setup a contract lease from the hostel to my self to apply for business rates in the hostel name.

I need help with the application and contract lease, I understand the change of use may require drawings or a simple application.