I'm sorry that you're finding this to be a more difficult process. I hope these 2 tips listed below help:
When on the Contacts page, you can click on the + sign next to Email Lists on the left and create a new list for every month or
You can add tags to each person based on their month date (you can do this via import or manually).
Then you can either send a monthly email to a birthday month list or you can filter a tag during a send to a different list.
Here is some information on how you can use tags.
I hope this helps!
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