Dive Center Management Tool

I want to start a side project related to managing dive centers. I know there are a few products but IMHO not good enough for the market.

An MVP it'll require a few months of development so I'm looking for advice validating the idea before investing time and money on coding.

I'm currently living on an island in Thailand which has more than 80 dive centers.

What would be a good strategy for validating this idea? Trying to sell the product before start coding?
PS: There is one person on the island selling an app built in Microsoft Access and he is selling the product on a year license basis.

Any advice will be much appreciated!