You can install Conga for Google Docs add-on from the Google Workspace Marketplace.
Prerequisite
Your Google account is active and you have the required permissions to install external add-ons. Contact your administrator for permission to use third-party add-ons in Google Docs.
Open a document and go to Extensions > Add-ons > Get add-ons. The Google Workspace Marketplace window appears.
Enter conga for google docsin the search box. Click the add-on tile from the search result.
Click Install next to the Conga for Google Docs add-on.
Review the terms of service and privacy policy and click Continue.
A message appears requesting access to data that the add-on needs to work. Read the message, then click Allow.
A confirmation message appears. Click Done.
Reload Google Docs to use the add-on.
Under the Extensions menu, you can see the Conga for Google Docs add-on. For more details on installing and uninstalling add-ons, see Google Workspace Add-ons.