How can i publish to a topic in iot core using lambda function?

Hi,

You can leverage sdk to publish payloads towards a iot core topic.

See below example (https://repost.aws/questions/QUyQP-7Ki6T2202ZHCZ-qkig/questions/QUyQP-7Ki6T2202ZHCZ-qkig/publish-to-iot-endpoint-of-other-account-iotdata-sdk-nodejs-lambda).

const iotData = new AWS.IotData({
      endpoint: 'xyz.com', // IoTEndpoint
      credentials: remoteCredentials
    });

    const data = await iotData.publish({
      topic: `topicfilter/data/clientId`,
      payload: JSON.stringify({event: 'something'}),
      qos: 1
    }).promise();

Documentation: https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/IotData.html

Hope it helps ;)