I was in the car wash business for over 10 years (express tunnels) my cars are hand washed only. Since purchasing the car in December it's been garage stored along with my other cars. Dealer is claiming that the front bumper has been repainted. Purchased the car with 70 miles on the odometer...
There are two bolts on each side of that piece. Mine was sagging a bit and I just loosened the bolts on one side and pushed the part towards the center of the car and re-tightened the bolts, then did the same to the other side. Pretty much fixed it, but my sag wasn't as big as yours. But worth a shot.
Halo sag. I brought this to attention in the link above several years ago.. Seems to be common. I believe the heat from the turbo and engine are to blame. Yours is definitely worse than mine. If you can get it reduced by playing with the bolts great. You might be able to get that part replaced with a new one but expensive and the problem will just occur again. I have been raising the engine hatch after driving to help dissipate the heat until the engine cools. Seems to have solved the problem as mine has not gotten any worse. Good luck!
I think the main issue with that part is that it's just pretty cheap plastic with no support in the middle. My car had the slight sag with delivery miles so I don't think that was turbo related. Also, since I fixed it over a year ago, it has not started to sag again (and I'm in hot Florida). Some folks have taken that part off completely - I have no idea if this is a good idea or not, as I'm not sure if that piece blocks water infiltration or if it's merely cosmetic.
It is cosmetic and really can't be seen unless looked for. I wiuld almost suggest to take it off if you are that worried about it until you sell. Only problem with this is you now have something else you have to keep up. Don't know about others but my basement is like the Bermuda Triangle and it may never be seen again.