I'm not sure I understand the question. If you wish to place components on the other side (solder side, which in Eagle I beleive is blue) then you can just click 'mirror' and then click the component or trace of your choice. The mirror cion, at least on my version looks a bit like like this "[ | ]"
I'll admit I don't have the latest version so I don't know if this has changed.
If you wish to put a group on the reverse, then highlight the group first, then click mirror, then right click the group and 'group: mirror'