Open SketchUp and select on the "Welcome to SketchUp" screen. In the License modal, ensure the Classic tab is selected.
You can use the SketchUp License Manager to retrieve your info by entering the email address associated with the original purchase. How to Authorize SketchUp Pro 2017 sketchup 2017 serial number and authorization code
For SketchUp Pro 2017, the license is categorized as a "Classic License". Unlike newer versions that use a Trimble ID login, this version requires two specific pieces of information for activation: Open SketchUp and select on the "Welcome to SketchUp" screen
Click and enter your serial number and authorization code exactly as they appear in your records. How to Authorize SketchUp Pro 2017 For SketchUp
If you have lost your credentials, there are three primary ways to recover them:
If you are transferring a license, you must first from the old machine before it can be successfully authorized on a second device. Important Legacy Support Information