Hi there!
Thanks for reaching out. I’d be happy to help with your question.
There is indeed a way to create an event series where the event occurs on the first Monday of the month. To do this, for “Event Series” choose “monthly.” Then for the “day” choose “a different day.” You will then see options to choose “first,” “last,” “second” etc of the month.
Here is a screenshot to illustrate exactly what that looks like:

Hope that helps! Please let me know if you have additional questions about this.
Thanks,
Sky