Delete data for touples for many records

Dear All

In out 7.1 SP6 MDM environment we have Customer repository. Last week we created an touple which is a look ou field to flat table with two fileds. Right after that we upload some data. Now our user would like to delete the old data and replace them with new ones. To perform that action I opened MDM Data Manager and from "Free-Form Search" I choosed records from my touples "Is Null - No". In that case I have list with all records I need to dete information in Tuple. I marked all the records and in "Record Detail" pane I wanted to simply press Delete button on my keyboard to delete tuple information. However that is not possible.

How can I "make" empty for multiple records touples information?

Thank you for help.

BR

Rafal