I know how to float a rigid body in fluid - I need to set “Feedback Scale” to 1.0 in the fluid solver, but it does not work for Organic Mass objects - they just go down disturbing the water, but they don't float.

I'm trying to apply Liquid Force to the Organic Mass object and fluid, but can't figure out how to do it.

When I click Fluid Force button, it asks to select the object:
“Select affected objects for Fluid Force. Press enter to accept selection”
I select the Organic Mass object in viewport and hit enter.
Then it asks for the fluid:
“Select Fluid Object for Fluid Force. Press enter to accept selection”
From this point I don't know how to do it. The fluid object is not selectable in the viewport.

How to do it exactly?