Plugin.js

const syntaxBigInt = require("@babel/plugin-syntax-bigint").default

module.exports = function (babel) {
  const types = babel.types

  const visitor = {
    BigIntLiteral(path) {
      const value = path.node.value
      path.replaceWith(
        types.callExpression(types.identifier("BigInt"), [types.StringLiteral(value)])
      )
    }
  }

  return {
    inherits: syntaxBigInt,
    visitor: {
      ...visitor
    }
  }
}