Re-writing the app using a web-centric development platform.

There is no natural path to go from an Access app that is usable on a LAN to
one that can be used over the internet.  If there were the web would be
littered with sites that look like Access applications and it most assuredly
is not.

The only path that doesn't involve an entire re-write in another development
platform is to allow Access to a Terminal Server on your LAN over the
internet (generally over a VPN) and have that PC host the Access app.  That
is practical for a limited number of users and not the general web-browsing
public.  In addition each of those users would need to be licensed for
connecting to the server, for Access itself, and for any other software that
the use of your application requires.