these are clovers. It's almost impossible to remove them one by one. I would simply remove a large patch of grass and weeds and replace that spot with new sod. However if the task is so huge, you could try increasing the nitrogen content of that particular spot by using high nitrogen fertilizers (use slow release). Be careful, high nitrogen fertilizers can burn grass so use slow release ones. It wil help reduce clover growth. I recall a patch in my yard not returning after such an increase of fertilizers.