Hey Ashleigh, welcome to the forums!
Good question. The best way to go about that would be adding CSS to your theme’s style.css file (or using the Simple Custom CSS plugin) that adjusts the size of the font for the link. Something like this:
.single-tribe_events #tribe-events-content .tribe-events-event-meta dd.tribe-events-event-url {
font-size: 20px; /* or whatever size you'd like */
}
I haven’t fully tested that, but it does seem to do the trick when trying it on my own test site. At the very least, that hopefully give you a baseline for how to make the adjustment.
Cheers!
Geoff