In your event dashboard, navigate to the registration website module:
Here, click on "general"
And then "virtual event app" where you can toggle on "Allow login from Registration Website to app"
Once this has been toggled, make sure you press "SAVE" at the top right hand side of your screen.
Now, refresh your registration site page and you will see a "LOGIN" button appear on the top right hand corner of your registration site (sample, as below). Guests can now directly access the virtual event app from the registration site by logging in here!