To answer this question we need to know little bit more.. How do you achieve in QlikSense last 12 months selection or (function)?
- Is it selection from Quick Calendar?
- Is it conditional Dimension?
- Is it Measure with SetAnalysis?
- Is it Measure with IF statement... etc...
Could you please post way you have achieved this in Qlik Sense so we can look for right soultion, otherwise it is difficult to say..