Violets do frequently invade lawns but without a picture we cannot identify your weed with certainly. Please attach a picture or two with your response and also indicate where you are located.

Thanks.
Picture attached below.

Thanks for the picture. This does indeed look like wild violet. Application of a broadleaf weed-killer should eiiminate the problem. It won't kill the grass. If you get a granular form, you can appy it with a spreader. Do this while the lawn is damp so that the grains stick to the violet leaves. You could also get broadlieaf weed-killer in a fall fertilizer mix and achieve two goals with one effort. Fall is the best time of year to fertilizer your lawn as grass will develop stronger roots with fall fertilization making a denser turf that is less susceptible to weed invasion. Note that violets are tenacious and several broadleaf weed-killer applications are likely to be needed over time for complete eradication.