Scared to repot tiny new orchids

[Rross]

Yesterday I bought 2 cattleyas (George King Serendipity and (Amy WakasugiYamanashi) and one dendrobium (Hiroshi Blue) sold in polypacks from a big hardware store. They’re potted in sphagnum moss, in 50cm tubes. I’m concerned that they’ll rot in this medium - there’s already a carpet of green moss on the surface of each one. However, the last time I repotted a cattleya this size, all its roots died. Can anyone advise me on what to do? Here’s a photo of two of them. The third is the same size.