I just told you above “how to”. If you never logged in to any of the SketchUp warehouse sites before, then you can use the login that you signed into this forum with, or use some other Google account (if you wish) or create a new Trimble account (if you wish.) The create account links should be on the login popup screen.
Unfortunately, if you manually installed all you previous extensions, and this was years ago, this all likely predated the “My Extension” feature that remembers what you install, and helps you to upgrade and migrate extensions to new versions.
So, to begin the process, you’ll need to login from within SketchUp, open the Extension Warehouse window, search and browse for extensions you wish to install, and install them.
Recommend that you restart SketchUp after the process of installing any extension(s).
From now on the EW will remember what you install under that login account, and in the future you can see a list of what you’ve installed under “My Extensions”.
P.S. - Get a small notebook or Steno pad to keep by your computer with account names, URLs, passwords and security answers. Then when you need to login to some account (especially from another computer, if say you main machine breaks down, then you have a record of the credentials.)
A hacker somewhere, malware accidentally installed, cannot hack a paper steno pad.