23, CO2 for mild under eye tightening & what can remove darkness? (Photos)

I’m 23 and have had fat transfer under eyes last year as I had deep set hollow under eyes. The results went well but I would still like to tighten up under one eye ever so slightly. I’ve seen videos for co2 when the laser hits and the skin shrinks. Is that permanent shrinkage? If so will co2 help my under eye. Also, I have darkness under my eyes that makes my eyes look more hollow than they actually are. The dark line casts a shadow on my under eyes. What can I do to get rid of it? Are there any lasers that can lighten it?