I don't understand the question.
Can you post a sample workbook that demonstrates what you are doing?
I can show you how to do this if you will upload a sample file. You will write a calculated field that defines a string based on the value of the dropdown. The calculated field is dragged to the Detail Shelf and then the tooltip is modified to include that field.
Here is one that I am currently using the:
"County: " + STR(attr([County]))+CHAR(10) +
"Count of Deaths: " + [subToolTip] +CHAR(10) +
"Deaths per 100,000 Residents: " + [subSubToolTip]+CHAR(10)+STR([SampleWarning])
This is the calculation for a field called ToolTip. I drag ToolTip to the ToolTip Shelf and then include it as the only tooltip item. It doesn't have to be the only thing there, but that is how I am doing this one.