Am I required to mail something to the defendant informing them of a default judgement before being able to collect?

The Judge says that the defendant has 30 days to respond and request a retrial. Is there anything that I should do, such as mailing something to inform the defendant of the default judgement within the 30 days?

Not necessarily but it depends on how you plan to go about trying to collect the judgment.

If I'm not mistaken, the court will notify them. It isn't your responsibility.