How to call restlet script using client script with TBA ?

You don't need TBA. Example of Client Script that Calls a RESTlet

But i want to call it using External Url which required tokens and account id< is any path available which i can use to call it.

Are you calling a restlet on a different account?

Yes

Ideally your client script should call an internal suitelet/restlet that makes the external call, otherwise you would be exposing the restlet credentials client side

That means there is no proper rule to call it using credentials

It's possible as long as you can generate the signature, I'm saying you generally don't want to do that client side

Ok, what is signature in it

This is an npm package, but the approach is similar.