Hi Manish,
What version of Excel are you using? If I recall correctly, the Microsoft Dynamics add-in works with Excel 2016 and Excel on the Web (with Office 365 business editions).
When you open your exported file, look at the pane on the right side of your Excel spreadsheet, and you will see the plugin. If you're not already signed in, you will need to sign in with your Business Central login and password. If you are not an Office 365 user, this will not work for you. (Also, if you have an Office 365 user login, but your admin has not assigned a license that contains access to Office apps like Excel, this will not work for you.)
Then, you will need to click on Refresh in the same Microsoft Dynamics pane on the right side in Excel, and this will fill your Excel spreadsheet with your Customers list.
I hope this helps. If my response has answered your question, please verify by clicking Yes next to "Did this answer your question?"