Before you proceed, you need Spaces installed on your phone.
How to add/change Description to Space?
Step 1 - Open the Space for which you want to add/Change Description and Click on the three-lined menu icon located on the top right corner of the screen.
Step 2 - SelectSettings.
Step 3 - Under the Description section, type/change the details that describe the Space. When you are done, click on the right tick button located on the top right corner.
You are done!