In the main toolbarclick on
the "Rubber
Stamp tool" icon.
Then in the properties
pane set
the "Size" of
the stamp radius in pixels e.g. "30".
Left click
on the image then reposition the cursor and left click
again to establish the direction and distance from
the sample area to the stamp
area.
Position the cursor over
the section of the image you want to edit then hold
down the left mouse
button and drag the cursor
to "stamp" the region
with pixels from
the sample area.