This weed is Lesser Trefoil.
If the clumps are small and few hand weeding may be practical taking care to remove the whole plant.
In most cases where Lesser Trefoil has been allowed to spread, chemical control will be necessary to control this weed. Choose a selective weed killers that lists Trefoil. One application is usually not enough, so repeat 6 weeks later if necessary for complete control of this weed.