Greetings,

To best assist you, can you please take a picture? You can then attach to your reply here and we can then identify and offer management options. 

I am attaching the photo you sent me here so that I can assign the question for identification/management. 

Hi there:

The weed in question is Redstem Filaree.

Control methods include good old hand pulling prior to flowers going to seed. Or, if you want to use a herbicide, you can apply a Broadleaf herbicide for infestations the lawn.  For larger areas where nothing else is growing, a nonselective herbicide is OK.  Please follow all instructions on the label and wear protective clothing when handling herbicides.  I've attached a information guide on the Redstem Filaree and a informative guide on when, how to treat all kinds of weeds in your home landscape. 

Redstem Filaree

Home Garden Landscape Weed Management Tactics

Hope you find this helpful.

You're welcome.