In order for you to be able to visualize your Funnel data by week or month in Data Studio you need to change the type setting of the Week number (ISO) and Month number fields imported from Funnel.
In Google Data Studio, start out by navigating to the Fields view for your Funnel data source. The week and month fields imported from Funnel are initially set to the type Text and now you need to change these to the Date & Time types ISO Week (ww) and Month (MM).
Changing the type for Week number (ISO):
Changing the type for Month number:
Once you've managed to change these field types you will find Week number (ISO) and Month number as available options when editing for example a line graph:
That's it, happy analysing!