The way the page looks has changed since this topic was started. To deauthorize all devices you sign into this page:
https://ecom-prd.trimblepaas.com/ecom/portal#/subscription
Choose My Products, then under the product you own, click View Included Applications. Then you will see a Manage Devices option for each product that is allowed two sign ins. SketchUp Pro is one example, click the manage devices link, then deauthorize all, and you will be able to sign in on the computer you’re trying to use.