OK, sorry I see the Alpha tag now. You can change the Trigger Out channel on the Preferences Page (the Alpha firmware receives and sends trigger messages on the same channel). Here’s the pertinent bit in the manual
Trigger Out (F5) – With F5 lit, the Groovesizer sends out pattern change messages. When the user changes a pattern in Trigger Mode on this device, any slaved Groovesizers will also change to the corresponding pattern (provided the slave has a pattern stored in that slot). The default MIDI channel for sending and receiving pattern trigger messages is 10. Change this to your desired channel by holding F5 and selecting the channel with Pot 6.