From the close reason:
See the How to Ask page for help clarifying this question.
The relevant bits:
Search, and research
Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!
If you ask a vague question, you’ll get a vague answer. But if you give us details and context, we can provide a useful answer.
The question could be vaguely answered with "you can do this with a RRULE" which is something you likely already know, but we don't know what you don't know. The RRULE is explained in RFC 5545 - Internet Calendaring and Scheduling Core Object Specification (iCalendar) so it would make no sense repeating all that. It's more useful if we know what part of it that you need help with.
I understand that not everyone wants to research RFCs, especially when you only do it once; this is why you might find the following resource useful to accomplish your task:
RRULE Generator Tool for Scheduling iCal Recurring Events
Whether you research the RFC, or search a solution with a generator; either way will yield you with a solution or a specific problem. In the latter case, you can tell us exactly how you don't succeed.
It might help to copy your question title to Google beforehand, it is how I found the generator tool.