Below are the various rule actions that the gtag extension enables within Launch. If you're unfamiliar with rule actions within Launch, check out the official Adobe documentation. To setup an action, you'll need to first create your rule, then under the actions select the "Google Global Site Tag (gtag)" extension, and then select the action type that matches what you want to do. A list of actions and links to their documentation can be found below.
The actions available with the gtag extension.
Preload the gtag.js library