You have purchased a license on Subscription for an Autodesk product and would like download one of the three previous releases of the product.
As a Subscription Member, you can download and activate the latest release, or any of the three previous releases, of most Autodesk products. You can activate one release of a product per license, purchased on Subscription.
To download the product software for which you are eligible, log into Subscription Center, select Access your subscription benefits, then Downloads.
From Autodesk - Autodesk Revit Architecture Services & Support - How to download a previous release of Autodesk software