在Lambda函数的环境变量中，设置AWS_SDK_LOAD_CONFIG为1，并将AWS_CONFIG_FILE和AWS_SHARED_CREDENTIALS_FILE分别设置为您的配置文件和凭据文件的路径。下面的示例设置了这些环境变量并使用AWS SDK for JavaScript访问S3：

const AWS = require('aws-sdk');

const s3 = new AWS.S3();
const bucketName = 'my-bucket';
const keyName = 'my-key';

exports.handler = async (event, context) => {
  try {
    const data = await s3.getObject({
      Bucket: bucketName,
      Key: keyName
    }).promise();
  
    console.log(`Object contents: ${data.Body.toString()}`);
  
    return {
      statusCode: 200,
      body: data.Body.toString()
    };
  } catch (err) {
    console.log(err);
  
    return {
      statusCode: 500,
      body: 'Error getting object from S3'
    };
  }
};

process.env.AWS_SDK_LOAD_CONFIG = 1;
process.env.AWS_CONFIG_FILE = './config.json';
process.env.AWS_SHARED_CREDENTIALS_FILE = './credentials';