Hey Priyanka,
You will have to add HTML text to create the buttons in the email template and use Deeplinks in order to carry out necessary actions (approve/reject) through microflows.
Kindly refer to the following for more information on rendering buttons.
https://forum.mendix.com/link/space/user-experience/questions/104587
https://forum.mendix.com/link/space/app-development/questions/108297