This is a particularly tricky weed to control :-) It spreads by rhizomes but primarily from seed and each individual flower can generate as many as 5000 seeds and they germinate very easily!!

The plants themselves tend to be somewhat resistant to most common lawn weed killers, so you need to search out one that that is specifically registered for oxalis control. And use with a sticker/surfactant as the leaves tend to be quite waxy and ther product may just wash off with irrigation or rainfall. And because of the rapidity of seed germination, multiple applications are generally required. If just small populations (one can only hope!!), manual removal is very efficient.

Once you have the worst of the adult population under control, you will want to use a pre-emergent herbicide to prevent the gratuitous germination of all the thousands of seeds waiting to pop into life.

The attached link has a pretty thorough explanation of the life cycle of this weed and various control options: creeping wood sorrel control