Hi,
first you should create a device for your DMX
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then in the Tools>controls>control>artnet
you can select one that corresponds to your setup ( here I'm using the Dmx Output Control Processor )
and now you can select the device
set the sending mode ( on trig, on change or continuous ) and select the channel
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and in the end, you can expose/link and learn the value field to control using your midi