Sadly there is no magic bullet for killing weeds in the flower bed. Anything that will kill the weeds will also kill the “good plants”. The are products like Preen that will prevent weed seeds from germinating but weeds that are coming up from an established roots system won’t be affected. Covering the weeds in between the plants with brown paper (like cut up leaf bags) with mulch on to of that will smother them but there is no spray weed killer that can safely be used in a flowerbed.