New to OpenHab - How do I fix my wish (Gardena Binding + Alexa file based)

Setup, Configuration and Use Beginners
5

You can create an item in an items file:

Number Gardena_Timer "Timer [%d]" { channel="gardena:ic24:home:myirigation:watering#watering_timer_1" }

And you can send a command in a rule to that item like so:

rule "Gardena"
when
    //sometrigger
then
    Gardena_Timer.sendCommand(20)
end

Now, Alexa doesn’t really support sending commands to number items but it can do Dimmer items
You need to set a tag of [Lighting] in the item and say:
“Set Gardena Timer to 20”

See:

It’s a work around.