To use Lowdown just like Greetbot, first login to your Lowdown dashboard here.
Once you're in, you'll see a box at the top for Welcome new members, press Edit Message.
A modal will pop up, simply press the toggle in the top right corner to turn on your welcome message. You can also choose to turn off the digest set up button and just use it as a welcome message.
Below it you'll see a preview of your message. Press Edit Text on the right to customise it to your liking.
<aside> 💡 If you'd like to use formatting you can be adding it just like you would in Slack's. Learn how to use Slack's mrkdwn language.
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When you're ready press Send Me a Test DM. This will send your message directly to you, and you alone in Slack so you can be sure you're happy with the formatting.
To learn more about why you should welcome your new members click here.