Sign in with your Emerald Club credentials on the Enterprise site. It’s in the upper right corner. You’ll need to select Emerald Club instead of Enterprise’s own loyalty program, which is the default.

Just to add, it’s a shared fleet, and if it’s a small location, might be moot, but anecdotally, I’ve generally received higher mileage vehicles at Enterprise. High-teens to high-twenties are the norm when I rent from Enterprise.