Small breast asymmetries after breast augmentation are usually the direct result of an asymmetry that was there before the surgery. If there is a pocket adjustment that needs to be made or little skin it needs to be taken out, both of these can easily be done. I recommend you follow up with your chosen plastic surgeon who can evaluate you. Good luck.
You did not post any photos and it is difficult o comment exactly. In general, I would say it is possible to be able to raise the low one.
Some mild asymmetry after implant augmentation should be expected. If it is a significant asymmetry, it then should be able to be fixed either with a capsulorrhaphy or breast lift.
In general, asymmertries of the breast implant position can be fixed with some internal suturing and/or work on the capsule surrounding the implant. Issues to go over with your Plastic Surgeon would be any asymmetries before surgery, hardening or capsule formation and overall expectations.
Best of luck.
Yes, it is likely that revisionary breast surgery will help improve your situation. Exactly what operation would be helpful will depend on your physical examination and goals. For example, some patients benefit from adjustment of the breast implant capsules (if bottoming out of breast implants is present); some patients benefit from breast lifting if the major concern is breast ptosis (sagging). Sometimes, several maneuvers are necessary to achieve patient's goals.
You may wish to post photographs with your next question for more specific advice. You may also find the attached link, dedicated to revisionary breast surgery concerns helpful to you as you learn more. Best wishes.