Where to modify libc path?

I want use other version libc ,so how to set path,

What exact platform are we talking about here? ARM? Like, wanting to use newlibc or something else?

You can add source code of needed libc as normal library by adding library.json to it.
Standart library will be overlapped.
To use yours custom libc in other included libraries, you should add it to dependencies.

Also you can add precompiled library to your project.