The consolidated app replaces what was called GitHub notifications. If you already have it, update to the latest version and your existing subscriptions keep working. The older GitHub app will be renamed GitHub (deprecated) and retired on November 16, so teams using Copilot in Teams through it have to install the new one.
To start, mention @GitHub in a channel or chat and follow the prompts to connect your account and pick a repository. GitHub's docs note that pull requests created from shared Teams context use the app identity, so repository rulesets may require an extra approval.

