The levers that are real
Reminders first, because they address the largest single cause. Email goes out automatically before the start, at intervals the product already knows are useful, and reaches everyone registered without you writing anything. The host can switch them off, which is the only control worth mentioning: leaving them on is the default and the cheapest improvement available. They are email, arriving in the inbox the registrant already gave you. Anyone promising reminders through a messaging channel to attendees is describing a different product from this one.
Then the access link, which solves the door rather than the memory. Each registrant receives their own private link in the confirmation, so arriving is one tap on a URL addressed to them personally rather than a search through old messages for a meeting address. A tight published agenda does the third part, giving someone a reason to pick the evening over the alternative. And a seat limit that is stated honestly does a quiet fourth: a room with a number in it reads as a real event with consequences, which is a different psychological object from an open link anyone could ignore.