As mentioned above - there is no surf in Singapore.
There are a large number of local first aid / life savers in Singapore which means the pay would not be that great, and employment options limited to a few International clubs or water parks.
There are a number of swimming coaches in the higher end (eg ex Olympic swimmers) but I don't know how much work they get - again a lot of local swimming coaches service he local market so the market for you would be predominantly expat and that market is already well serviced.
There are a lot of fitness coaches/personal trainers here already and some seem to make quite good money. it is a different skill set but might be suitable.
katbh mentioned
International Schools which would be a good option but you may need training or certificates.
As a pro coach in Surf Life Saving you would realise that a pro coach in another sport would not be as good a coach in SLS as you are, so you have to realise you would be that "other sport's coach" here. Look to where your strengths are and then think of what scenarios would want those skills. You have not put much in the post for us to give much advice.