If the down coat is monochrome, it can be mended with a needle and thread, but the needles needed for the down clothes are special. The very fine needles can be done. We do not use the needles at home at ordinary times. The needles are too thick. After the stitches are too thick, they will leak the hair. If there are no fine needles in the house, it is best for the skilled craftsman to choose the same material to help you mend it.
You can find the same color fabric at home, cut out a cloth that is slightly larger than the hole, and then sew it up with a sewing machine.
There is a kind of applique for repairing eiderdown, buy a towel over it and iron it on it, then it can be pasted.
If it is the upper position of the down jacket, you can buy yourself a logo. The size should be possible to cover the crack as much as possible. If it’s a large brand of duck’s down coat, it can be sent to the factory for repair.