Cubasis Sustain Filter for a Channel

Hello there.
I have Cubasis for iPad Pro and several instruments installed. For example, my MIDI keyboard simultaneously sends signals to channel 9 and channel 4 (to play two sounds together). Channel 9 is Piano, and Channel 4 is Strings. But I want to use the Sustain Pedal only for Channel 9, not for Channel 4. How can I filter the Sustain signal for Channel 4? Note: Pino is different Instrument (Ravenscroft 275) and String is the Module by Korg)