Semi ripe/softwood cuttings in mid to late summer works - method mentioned in this link
https://www.gardeningknowhow.com/ornamental/shrubs/japanese-andromeda/propagating-pieris-plants.htm

The species, but not all varieties, may grow from seed - the other way is by layering, pegging down low growth into the soil or a pot and waiting for roots to form.

I propagated one of mine by the layering method into the soil I just made a little nick in the stem,and pegged it down.It took a while,so you will need to be patient..I potted it up in Ericaceous compost,till it was big enough to plant in a border. It is now as big as the parent ,some years later..Mine is Pieris Forest Flame too.good luck :o)

Thank you for your advice. I will try this and let you know what happens.