Go to App Manager (you can search it under Quick Find).
Click on New Connected App.
Name your app appropriately - to indicate that Glean will have access to this data - eg. “Glean Sales App”
Enable Oauth Settings and under callback URL - copy over the callback URL from the Authentication section of the SOQL Action page.
Ensure Use digital signature is unchecked.
Add api and refresh_token, offline_access scopes.
Remember to Uncheck “Require Proof Key for Code Exchange (PKCE) Extension for Supported Authorization Flows”.
Hit Save.
From API > Consumer Key and Secret, click Manage Consumer Details and copy the Consumer Key and Consumer Secret on to the SOQL Action page.
Under Manage Apps > Connected Apps, find your app and under OAuth Policies make sure that in Permitted Users you have selected ‘All users may self-authorize’