Ask the developer of the app you are using.
What you are asking is beyond the scope of this forum, and you should have instructions from the App creator on what to do.
Or if you are using an oculus, just use oculus Dash and snap an open chat window in place.
Or generally people use OVR Toolkit, and that does the same (but works on all headsets), it’ll grab an existing window thats open on your computer and pin it to your hand.