If you can unmark the checkbox directly on the IRA Information Worksheet without doing an override, that won't cause any problems. It just means that you answered incorrectly at some point when TurboTax asked if you were covered by a workplace retirement plan.
If TurboTax won't let you unmark that checkbox without doing an override, it means that TurboTax is inferring that you are covered by a workplace retirement plan based on box 13 of your W-2, box 13 of your spouse's W-2, or you made a contribution to a self-employed retirement plan.
