Hello, my name is Humberto Valle and I focus on growth strategy and marketing for companies around the world, i run an all inclusive digital marketing platform with a team out of Arizona.
Here is my feedback:
This is not an ideal situation you want to be in. Just as with crowdfunding campaigns many people wait until they are 'live' to promote. Strategically you need to have been prepping and laying the ground work for the brand and launch prior to the launch itself. When the launch is live your focus then is to reengage prior interests, drive referrals and shares, and closing on sales or donations.
We're here now, so my plan would probably consist on heavily emailing and building a list of reporters locally that I can reach out with a pre-written press release (learn how to press releases) while simultaneously running paid advertisement campaigns on the appropriate target market's social platforms (not every company benefits from facebook, or insta, or google, twitter, etc) learn your demographic and be where they are - it could easily even be an app that you are not aware of. but because of the time sensitivity of the launch you need to have paid content now as well.
capture as many leads as possible with these paid ads, with a/b testing and retargeting.
reach out to old contacts who have been introduced to your project while it was still being developed and ask for support with a share, a like, a free trial, etc. offer heavy discounts if needed for purchases.

Kind of broad ideas but it gives you a sense of direction, at least I hope I did lol

This depends entirely on who you're launching to and what. If you're launching a consumer service, I'd focus on getting exposure for your launch and making sure the product works for all users who try it. There might be other elements to this depending on what the product is. One thing I would definitely do is to learn from your first users, have conversations with them and understand why they decided to try your product and what they think of it.

Receiving feedback from your clients/customers. Engaging with them as much as possible. Learning about things that worked and didn't work so you can tweak your product or offering for their actual needs vs. what they or you thought they wanted/needed.