If it's really overly bad, then there are 6 screws that hold the barrel and hop into the gun, in the upper half of it.
The front pin that holds the gun together goes through a part of the barrel assembly, so if those 6 screws are loose, then the wobble will come from that.
Pop the pins, take the buttplate off, hinge the gun open using the safety switch at the front end as the pivot point, then once upper and lower are apart, pull back on the lower and it'll come off.
Then check the 6 screws in the upper - two are at the front at the back of the handguard, and there are 4 in a rectangle configuation just ahead of the feed tube on the hop unit.
If it's a new gun then they ought to have some blue loctite on them holding them in, so it's odd that they'd come loose, but you never know.
Tightening them and then reassembling ought to sort it out, I never really noticed any particularly bad wobble in my ICS.
