As the displacement must be small, if you can work within earshot of someone watching the Telly, the easiest thing to do is gently push the LNB arm to flex it left, then right, then up, then down.
One of those actions will restore full glory and the others will make it worse.
And then you will know which way to very very careful move the dish a mm or two.
ie If LNB arm up creates improvement, then moving the dish down is the answer
Ditto LNB arm left = dish right (Signals are reflected off the dish surface, so everything is opposite)
So, gentle pressure on the arm (without blocking the dish, obviously!!), work out which way the dish has to go, then I suggest a gentle (very gentle) shove until happy, then gently tweak a bit more torque on the bolts so it doesn't move again.
This method should work as the bolts are clearly not tight enough right now, so you should be able to make use of that fact and effectively create the desired small movement against some resistance.
