Can't find a way to open on a other display

Hello,

we are using i3 as window manager.
We want to open/moven onboard on the other monitor, but we can't find any option for that.
We also tried if onboard always open on the primary monitor, but that is not the case.
Also it's not possible to move onboard to a other monitor with the i3 build in commands (because i3 can't find onboard as window (wmctrl -l).

How could we decide on which monitor onboard will be opened ?

We don't(!) using onboard with the dock option, the keyboard should be above the applications.

I hope anybody can help us, thanks!