In order to install the Revit integration for Sigma Estimates, you need to have Sigma Estimates Enterprise installed as well as Revit (or at least the Revit Viewer).
For Sigma Enterprise: https://sigmaestimates.com/
For Revit: go here
1. The Revit integration for Sigma Estimates can be found in the Sigma Shop.
2. The Shop is located here: https://sigmashop.sigmaestimates.com/
3. Once you download and save the installation file to your desktop, double click the file to run it.
4. During the installation a window will open asking you which installation / edition of Revit you want to install the integration in to. Select the appropriate version, and click OK.
5. Once the installation of the integration is complete, a Sigma Estimates tab will be shown in the Revit tool bar.