Are the revised brand names updated on your raw data or have they been edited within the dimensions area?
You can drag [Brand List] to the Filters card and exclude ABC. This will get rid of the redundancy
If you want to merge and treat ABC and A_B_C as one
you can either use groups
or a calculated formula to replace the Underscore _ and have the names as they were previously.
If you want to exclude the old names add the field to filter and exclude the desired brands