For some software to work properly like IDM (Internet download manager), the extension of the software is need to be added to google chrome.
The extension is by default is added to the google chrome after installation , but if we click disable it and delete it from the extension gets deleted from the google extension
So to add the extension again follow the steps given below :
First of all open google chrome
And click extensions.
Then open the installation / destination folder where the software is installed of which extension is to be added.
Search for .crx format in the folder
Then open google chrome beside it.
Drag the crx file to google extension and put it in google chrome as shown in pic.
Then click add extension option , it will get added.
Then enable it.