If you're in a dataview with one entity A and you need an associated entity B in your microflow, pass entity A to the microflow and then do a retrieve over association to retrieve entity B. You'll then have Entity B to work with in your microflow.
You can only pass the context to the microflow from a page. If you need to use the associated entity just do a retrieve in the microflow based on that association and it should work.
You can also try to create a new microflow on the button of that page and Mendix will automatically pass whatever context objects are available for that page and accessible for that button.
Hope this helps.