Reporting Services Filter Years

Reporting Services Filter Years

I would like to filter the information on a report chart, so it shows the
data since one and a half years ago, until the present month. I already
have a parameter which is chosen by the user to be used as the month of
"today". Now i'm using the filter option in the query designer, but i
would like this to be done in an automatic way.
My Time dimension is structured like this:
in which año is year, mes y month, and these two are grouped.
How can i do this filter in an automatic way, according to the parameter
already chosed by the user?