Explanation
Customize Customer Service workspace
You can use your browser's developer tools to customize some aspects of the Customer Service workspace.
Turn on the enhanced multisession workspace (preview)
With Customer Service workspace open, press the F12 key to open the developer tools window.
In the console window, type the following command and press Enter:
Xrm.Utility.getGlobalContext().saveSettingValue("msdyn_MultiSessionLayoutImprovements",true) Refresh the app page.
Note: If you turn on the enhanced multisession workspace, the enhanced experience applies in both Customer Service workspace and Omnichannel for Customer Service.
Reference:
https://docs.microsoft.com/en-us/dynamics365/customer-service/csw-overview#turn-on-the-enhanced-multisessi
https://docs.microsoft.com/en-us/dynamics365/customer-service/csw-overview#simplify-navigation-in-customer