the are 4-6 locking slot tabs on the bumper cover that lock into slots on the black grill pieces. 2 on the top, two on the bottom and one on each side IIRC. You can try to pull the grill forward to re-lock into those tabs into place. Otherwise the best way to make sure they are reattached is to pull the front bumper cover (~ 25 min ) and reattached from back side. You may be required to do this none the less as one or more of the tabs could have been torn off when it was pushed in. If so, just reattach the grills using a hot glue gun. Do a search on radiator cleaning and you'll find plenty of DIYs for bumper cover removal.
Tough to tell from this pic (it's all I have) but if you zoom in on the lower left, you'll see the receiver tabs on the grill pieces and can partially see a male tab from the bumper cover....
Good Luck
