Filter between multiple datasets

Hi all,

So basically I have two data sets which contain row level data, using the option of 'Filter using related data sources' doesnt work for some unknown reason, I am trying to filter on the date so for example I have 13 months worth of data in the dashboard, I want to select January 2019, this changes the sheets which are related to this source however not the ones on the other source.

I understand I can do this via a parameter however not entirely sure how to do it, as the Month within the data would need to be called 'December 2019' and currently the data is in the format of 01/12/2019,02/12/2019 etc so this wouldnt work. I had the idea of using DateTrunc(mydate) to get 01/01/2019 and then using this as my parameter however unsure how that would work.

Can anyone help?

Thanks

Paul