Between Dates update field

Between Dates update field

Hi, 

I have a series of dates ranging over the next 3 years within the contacts module, and have a picklist for each month for example April 2023, May 2023, June 2023, I can do a workflow for this, however it will mean I have a few in place as I can only have 8 conditions. 

Can I do this via function, upon Date 1(date field) and Month (Picklist) and for it to work on the basis, for examepl, if date 1 is between 01/01/2023 and 30/01/2023 change month to January 2023, if date 1 is between 01/02/2023 and 28/02/023 change month to February 2023 and so on?

Where shall I start?

Thanks

Ant