Select the workspace where you'd want the app installed.
Copy and paste the YAML file into the app manifest field. You can create a YAML file in the export interface.
Click 'Create'
Do NOT click 'Install the App to Workspace.' Due to how Slack configures authentication, the application won't work. Instead, scroll down to App Credentials and find the Client ID, Client Secret, and Signing Secret.
Save those credentials in Export View.
Install the Slack app in your workspace.
Don't forget to publish your project! Your users will only be able to interact with the most recently published version of your project, not your project's drafts.