Convert week numbers into months

Hi. How do I convert week values into months? Note, the original data is not a date, simply a value specifying the fiscal week. I would like to know how to convert these weeks into months e.g. week 1, 2, 3, 4 all = Jan, etc.

There are several posts similar to this issue but they are not quite the same. I have a column of week numbers and years e.g. 01.2019, 02.2019 etc. these are not formatted as dates. I have split these out into separate columns of week no. and year, but now want to reference this data to a separate table that only has data summarised. in columns. by month e.g. April 2019. 

I believe the simplest solution is to add a column to the first set of data which indicates what month a week falls into, and then (hopefully) compare these figures to the separate table of monthly figures.  

Apologies if I have made some basic errors in my approach to this, I am new to this, so please feel free to recommend alternative approaches. 

Thanks