Tier-1 slicer overrides Tier-2 slicer

[LTO]

I have 2 categorical slicers in a schema, AB filters AB2. They are both working.

But While I am in AB2 and have "B1" selected, if I Select "A"  in AB, I would like "A" to override my current selection in AB2. In other words, AB2 should give me "A1, A2, A3" instead of  "A1, A2, A3, B1".

I have created a Key Table for AB, but still no luck.  I prefers it to be worked out in DAX in order to build on for the future.

 Thank you so much in advance!