Login to My Esri. From the home screen, click on the "My Organization" tab. Then click on the "Products" tab. Under the "Downloads" menu on the left-hand side, you will see all available downloads for your organization. ArcGIS Pro will be included as an available download if your organization has ArcGIS for Desktop licenses that are current on maintenance.
Once you have downloaded the file, be sure to make it internally available for your end users to install onto all the machines that they plan to use ArcGIS Pro on.