Go to your Google Account at myaccount.google.com
Sign in if needed
Open Security
Under Your devices, select Manage all devices
Review the list of devices signed in to your account
Select each device you want to remove
Click Sign out
Repeat for all devices you want to log out of
Change your Google Account password
Turn on 2-Step Verification
Review third-party app access and remove anything unfamiliar
Check recovery email and phone number for accuracy
Sign out of Google in each browser and app if still logged in
Clear saved passwords from devices you no longer use