We use concat option of data tab, which can then be pulled in dashboard.

if I’m understanding it correctly. you want to merge the multiple response into one bucket. e.g. if respondent respond scale 9 or 10, you want to show promotor, for 7 or 8 you want to show passive and 0 to 6 you want to show detractor. if it is correct, then you can do this in two ways.

first way:

directly from survey data: Open survey > Data & Analysis > Field Editor > Create Field > Bucketing

Enter name of Field: Select Question from dropdown and the create bucket accordingly. Then add the same variable in your dashboard database and use that variable for your visualization.

second way: 

From Dashboard: Open dashboard > Settings > Add New field after clicking (Add Field) and make it as text set (do not use existing field) > Enter name of field > Then map your question from dropdown

 

Click on variable setting > manage Label

Remove all the existing labels and add new label as per requirement.
 

Then assign labels to source code and save it.

Then you can use same field into your dashboard.

if you want to merge two or more column’s data, then you can Open survey > Data & Analysis > Field Editor > Create Field > Combine > Concat (default option). You can delimit response with any character.

Thanks for your help @Shashi and @ArunDubey !