If you are using SketchUp 2018 and want to sign in, you need to create a Trimble ID. That can be your Google email if you want, it can be any email, but usually the one that you have used in the past for Extension Warehouse and 3D Warehouse.
If your email is handled by Microsoft it can be a challenge to find the password reset emails. See if the steps I gave here will let you find the emails: