There are two groups that you could be talking about so I’ll describe both.
On the mixer:
There is a spot where you can route 40 different sources to the ME-1/500’s. These sources can be inputs, outputs, groups, fx, mains, etc.
For the SQ; Output patch > ME
Page 17: https://www.allen-heath.com/media/SQ_ReferenceGuide_V1_2_0.pdf
On the ME-1:
You can set the mix button 1-16 to: group, aux, auto, 1kHz sine, ch1-40.
For the ME-1; shift menu > select key 1-16 > select mode (group) > assign members > exit menu mode > press key > click group button > adjust according to needs.
Page 24 & 18:
https://www.allen-heath.com/media/ME-1-User-Guide-AP8997_3.pdf