If you already owned SketchUp 2017 Pro and simply need to find your old details, or if you are looking for the free version, here is the official path:
: Your license information was sent to you at the time of purchase from sketchupmail@sketchup.com . It includes your registered Serial Number Authorization Number License Manager Tool : You can look up your active license information on the SketchUp License Manager Sketchup 2017 License Key And Authorization Number
Finding your license details depends on whether you have the software currently installed or need to retrieve it from your records. Since 2017 is a "Classic" version (non-subscription), it requires a specific alphanumeric Serial Number and Authorization Number to activate. Where to Find Your Existing License If you already owned SketchUp 2017 Pro and
On the "Welcome to SketchUp" splash screen, click the License tab on the left. Add License: Click the Add License button. Where to Find Your Existing License On the
If purchased through a third party, contact them directly; they often provide license details as a Word document or email attachment.
How do i get an authorization code to update my SketchUp 2017