Add Custom Field below the checkbox

You can do this with the Woocommerce functionality.
So, you can do it with code or a plugin.
With Code:
https://woocommerce.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/
https://www.tychesoftwares.com/how-to-add-custom-fields-on-woocommerce-checkout-page/
With plugin:
https://www.wpdesk.net/blog/custom-fields-woocommerce-checkout/

Maybe in the future, we will implement this feature in a premium version of our plugin.

Thanks for using our plugin

One MOre question can we add one more checkbox with 0 prices so user select choose 0 or 5
how we can achieve this

I have done this task

Great