Dear Oleksandr, thanks for posting this interesting technical question on RG. Personally I never worked with this software, but it might be worth having a look at the following potentially useful tutorial video:
In the last Rietveld refinement, in the General section of phases selects the type of map (2*[Fo-Fc]) in the Fourirer Map control. Then choose the reflection sets, the ones associated with the powder diffraction pattern. Finally, appear the rhomax and rhomin in the command windows .