TBH I'm at a loss as to what your after or why you have a problem if the bloke set it up for you.
I will cover what I know of it and let me know how this fits with what you have.
To start with multi room uses a dual lnb, this saves having additional dishes put up, now from that lnb you should have 2 coax leads running to your house, 1 lead to your original sky box as you currently have, and the other lead going to the room with the extra sky box that you will use as your multi room device.
The installer should of aligned the lnb to the correct alignment for you to receive the broadcast, both sky boxes should have their own viewing card and work totally independent of each other allowing them to watch different channels at the same time, that is what you pay your multi room subscription for, only extra thing he should of done at this point if it's anything like the original install is the card needs to be paired with the unit, but the install bloke should of done all this for you, by the time they leave you should have sky on BOTH boxes\TV's.
Do NOT adjust the lnb or you will knock it out of alignment, if your original install has good picture\reception then that side of it is fine.
Go into the Services menu and select 4, system set up, now press 6, signal test, both bars should be around 2 thirds of the way across, on mine the top bar is slightly further over, there is a health check option as well that is pin protected, never used it so don't know anything about it so can't say anything there.
Where did you get it from ? sky or some reseller ?
But TBH any problems should really be aimed at the person who installed it if they did it wrong, otherwise you need to contact sky with your problem and they should be able to tell you what to do, are you actually getting anything on either of the boxes ? if you are on the main and are not on the new install then you may well need to contact sky to activate that new install possibly ?
Hope this helps a bit anyway.