why my dimmer in the kithen also dims lights in another room
Sounds as though the feed for your other room is simply connected to the wrong side of the kitchen dimmer switch.  The kitchen dimmer is in series with the other room dimmer.  This was presumably deliberate at the time.

Move the connections that feed the other room to the other side of the kitchen dimmer.  This will take the kitchen dimmer out of the other room's circuit.