How to create a multi-select dropdown containing a list of dates based on a numeric field (day of month) in record

I have an app that allows my content writers to log and plan content they have written for a client's website. I need to add a field that allows the writer to select which deliverable cycle the piece of content is for. Each client in our system has a `content deliverable cycle day of month` field, which is basically a numeric field that takes input between 1-28. If the value = 5, then the following deliverable cycles would need to be in the dropdown:

Jan 5, 2021
Feb 5, 2021
Mar 5, 2021
Apr 5, 2021
May 5, 2021
.... and so on (maybe show 6 months before and after current monthly content deliverable cycle)

If everyone's cycle started in the first half of the month, I would just have a static month selector, but some clients cycles start on the 25th, which would be confusing in that case.

Thanks in advance!

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Matt Makris
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