Hi @ranjitcool, if you have root access to the server where your site is hosted, you can create a cron job that periodically runs certbot renew to renew your certificates automatically.
Please see https://certbot.eff.org/ to learn about how to install Certbot with your particular web server and OS.
If you don’t have root access to the server or aren’t familiar with the system administration concepts that the site describes, it might be a fair amount of manual effort for you to use Let’s Encrypt and you might want to ask your hosting provider to integrate it instead.