If an individual has been denied admission into the U.S. by U.S. Customs & Border Protection, solely under INA §212(a)(7), they would not require a waiver to overcome the inadmissibility.
An individual being denied under INA §212(a)(7) may have failed to establish their eligibility to enter the U.S. in the status they are seeking. Generally, this occurs with individuals attempting to enter the U.S. as visitors in B-1/B-2 status - they may fail to establish that they are truly entering the U.S. to engage in permissible B-1/B-2 activities and accordingly, as denied admission.
How do you fix this? While it generally depends on the facts of your case, it would be best to confirm that you do in fact qualify to enter the U.S. as a visitor based on your proposed activities. In addition, you should be able to demonstrate your strong ties outside the U.S. (employment, residence, financial ability to support yourself while in the U.S. without engaging in unauthorized employment).
On the other hand, if an individual is denied admission into the U.S. under INA §212(a)(7) and another ground of inadmissibility (fraud, criminal conviction, etc.) or issued an Expedited Order of Removal, they would need a waiver to overcome the other ground of inadmissibility.