I have a dent on my left buttock from falling down friends stairs. Would squats and exercise help with the dent and also time?

I think you meant "Would squats, exercise, and also time help with the dent?" But since this is not about grammar, I do believe I know what you are asking.
The answer is that the dent is due to injury to the more fragile fat cells than the more robust muscle cells. Some the injured fat dies, and after the dead cells are reabsorbed, a dent remains. This dent is in the fatty layer, so exercising the muscle will not help, even if you do as many squats as a body builder. 
Time may help scar tissue retraction diminish a bit (as scar stretches and matures), but this too will not "fix" the dent. 
Only fat grafting (more than once at 3 month intervals, usually) can replace the damaged area of fat with your own living fat cells. Squirting in a big blob of fat will NOT work, except to give a large dead fat oil cyst and perhaps more scar tissue and indentation. Proper grafting in well-vascularized tunnels will allow the maximum graft "take," usually no more than about 50%. Thus, this may need to be repeated, and since it takes the body time to remove the dead fat cells, you should wait to see just how much lives and how much (and exactly where) dies.
Find an ABPS-certified plastic surgeon who is experienced in fat grafting. This is a straight forward procedure done under local anesthesia. Best wishes for a smooth butt! Dr. Tholen

It is very difficult to determine the exact size and shape implant you will require to best match your ideal butt image without an examination by a board certified plastic surgeon. Not just any board certified plastic surgeon, but one with many years of frequently performing breast augmentation surgery including different approaches, techniques and implant choices. This is because several measurements not to mention your breast characteristics are needed to determine the optimal implant size to obtain your goals. Without knowing these dimensions it would be difficult to make this determination. For example, the existing base width of your buttock will determine, in many cases, the maximal volume per implant profile that you can accommodate. Liposuction of your lower back and fat transfer is also helpful as an adjunct to implants. Using “want to be” photos however are useful if simply provided to the surgeon.

Without a photo it is hard to determine what would be your best option. It is unlikely that squats will correct it, you may need some fat grafting.

Dear taylorb13,it is not likely that squats will help you with your indent. It would be the best to consult a board-certified plastic surgeon.Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery