Filters are used to limit the data in the table that underlies each viz - when you "select January" only january data is available in the table
So what to do - the typical approach is to use a parameter (v filter) to select the end month then use calculations to see the chosen month and the previous
If this posts assists in resolving the question, please mark it helpful or as the 'correct answer' if it resolves the question. This will help other users find the same answer/resolution. Thank you.