They announced the First Mile Event Tour and put a banner across the top of the Rivian website with a link to sign up. It's a pop up banner, so check your web browser settings to see if pop ups are blocked.
I believe they will send invitations to preorder holders that live near the cities that are having the events. There are a limited number of time slots, so I'm sure they fill up fast.
It has always been a mystery to me, as to how they determine the order of guide contacts or drive event invitations. I understand that configuration and living near a service center is important, along with the date you preordered. You would think that if you placed a preorder for an R1T, LE and live near a service center, that the date you placed the preorder would be the only fair way to determine who is contacted first. From what I have seen on this forum and others, the preorder date isn't as important as I thought. It doesn't make sense that color selection would have any affect on when you are contacted, since that can be changed before finalizing the order.
I ordered an R1T, LE on the first day, 11-26-2018 and live close to the factory in Normal, but I have not had a guide contact and I didn't receive the email for the drive event. I contacted CS within hours after the first drive event invitations went out and I was told they sent me an invite. I never received it, but I always get other email announcements from Rivian. Fortunately they were able to help me secure a spot for a test drive. I'm guessing the slots for the week of Sept 26-30 are all full now.
I'm hoping they continue to schedule new drive events now that they are ready to start deliveries.