If you wish to take control of your account and sign it out of other devices, you can follow the steps below.
- Under Account settings, tap on Content and Devices. 
- Next, switch to the Devices subtab and go to the app you wish to deregister the device from, and tap on Deregister. 
Method 2- Using the Compromised Account Feature
- Tap on Login and Security. 
- Sign In to your account if required. 
- Tap on Start under Compromised Account and follow the on-screen instructions. 
Method 3- Log Out By Changing Your Password
2. Under the Password Section, tap on Edit, and follow the on-screen instructions.
Once your password is changed, you will be logged out of all your previous devices.
Method 4- By Adding 2-Factor Authentication
- Go to Settings from the hamburger menu present under the bottom right corner of the screen.
- Under the settings menu, tap on Sign Out.
This will immediately sign out your amazon account from the said device.
- Tap on Customer Service under the same hamburger menu. 
- Scroll down and tap on Chat with Us. You may also choose to receive a call back for assistance. 
Wrapping Up
Also, Read the following: