One doesn't "convert" an Access form to run in a browser. Microsoft tried to do that at least three times, unsuccessfully.
What you can do is migrate the data from your Access tables to a database that supports the brower/web environment, as Plog noted.
Then you can acquire and learn some sort of web development language to create web pages that will run in the browser.
PHP is an option, but so are various other .net framework development languages, C#, VB.Net, JavaScript and a startling array of flavors among them.
Still another option, which you might consider depending on your organization's environment, could be PowerApps.
See this series of videos on one example of a Hybrid application which has a SQL Azure backend, an Access interface and a PowerApps interface.
As Pat noted, and I should have included, the "heavy lifting" is, and always will be, done in the Access interface.