Contact
One address, read by a person: hello@excel-lessons.com.
A step marked you wrong
Say which lesson, which step, and exactly what you typed. The marking is done by the same engine for everybody, so if it was wrong for you it is wrong for everyone, and the fix goes into the lesson.
A lesson you want
Tell us the job you were trying to do in Excel when you got stuck. A lesson is built from a real task, not from a function name, so the task is the useful part.
A team
Seats for a team, with progress you can see, are on the way. Write to hello@excel-lessons.com with how many people and what they need to be able to do, and you will hear back before it launches.
Your data
A copy of what is held about you, and the button that deletes all of it, are on your account page. If you cannot sign in, write to privacy@excel-lessons.com from the address on the account. What is collected, and why, is on the privacy page.