The easiest way to do this: Just respond to that first email. A simple “hey” or “hi” will do. Or, if you wanna do me a huge solid… tell me how you heard about the course!
Here are some less easy ways to do this:
https://www.loom.com/share/4af03ee1b6ca4fa3a240aba6c6f6e497
https://www.loom.com/share/f215cd70824b4f09aef44b89c7d02b7a
As soon as you're done with this little task, the next email should be arriving in 3... 2... 1...