Oracle Forms

Hi,

I am having 2 canvas both content canvas in one form.
There are lov dropdowns to get the values and when queried we get result set in plsql table type.
Both the canvas are identical and value from result set of one canvas get populate on the other canvas.(same lov selected values)
can anybody tell how to clear the second canvas without exiting from the canvas so that if i want to select new lov i can be able to do that?
what trigger can i use to clear only the values of the lov on the sceond canvas and not the whole form(like we use clear_form).

Thanks,
Mandar.