yarn add @substrate/txwrapper-substrate

In a JS/TS index file of package:

import { methods as substrateMethods } from '@substrate/txwrapper-substrate';

// Export methods of substrate pallets included in the chain's runtime.
export const methods = {
    balances: substrateMethods.balances,
    utility: substrateMethods.utility,
    proxy: substrateMethods.proxy,
  };

Have a look at the txwrapper creation guide for chain builders to see more guidance on how to use this package in a chain specific txwrapper.