If you've still got the Ignite 2017 app installed on your phone and you're waiting for this year's update, it's not coming. For Ignite 2018, you'll need the MSFT Events app, an app for iOS and Android that's meant to consolidate all Microsoft events.
The app first arrived in early July for events like Inspire, and it's once again been updated for Ignite and Envision. It has the following features, which you would have previously found in the Ignite app:
My Conference – See your Microsoft Ignite schedule and favorited items.
Schedule Builder – Search for and sign up for Microsoft Ignite sessions.
Recommendations – Get personalized recommendations based on your interests.
Attendee Directory – See and connect with other attendees who have opted into the network.
Session/Speaker Details – Review details about specific sessions and speakers.
It's only available for iOS and Android, so there's no app for Windows 10. The iOS version does support iPads, so if you're using an LTE tablet to navigate the conference, you'll probably want to bring an iPad instead of a Surface Pro.
You can expect Microsoft to use the MSFT Events app for future events as well. The Build app, which hasn't been updated since 2017 on Windows, will likely not be updated for 2019.