Crosstab Filtering/Prompt Help

[RRCognos23]

I have a cross tab with 4 members as columns along with sub members from another dimension within the first 3 column members and an the an level under the last member (from which the other 3 sub members came from). I want to be able to filter on the level while keeping the members of the first 3 columns the same. I have another dimension level as my rows as well as a measure. How would I go about doing this? I created a prompt to try to do this but it ended up filtering all sub members rather than the last.

I am fairly new to Cognos so I apologize if my lingo is incorrect. Also let me know if there is a better way to go about this. I'm using a DMR model but I have a Relational model with the same dimensions as well. I also have one prompt already that filters this information based on a separate dimension.

Thank you