Here are some suggestions.
(1) Do your Management Course
(2) Dive a lot all over the world in different environments
(3) Become a DM or Instructor and interact with customers in dive resort
(4) Get information about dive retail business
(5) Oversee day to day operation and dive expeditions
(6) Manage logistics for a busy operation
(7) Gain knowledge of dive equipment servicing
(8) Gain Knowledge about dive boat, operation, maintenance, operating cost etc
(9) Gain knowledge about local permits, regulations, taxes etc
(10) Gain knowledge of marketing dive package, dive tourism etc.
or
Do a Dive resort Managers course at Mermaids Pattaya, Thailand
Bottom line , if you don't enjoy diving as much as your customers you won't be successfull as Dive Resort Manager.
This just my stupid opinion.