How to decrypt SD card

[Windows Central Question]

I encrypted my SD card enabling the option provided under setting in latest build 15007:1000 on my lumia 730.. I later downgraded my phone as the build was very buggy, i forgot to disable the encrypt sd card before downgrading.. Now my sd card has got locked.. Unable to access it on pc, or any phone.. What should i do so that i can get my sd card and all its data back.. I cant format as i have my data in it.. Pls see- i m trying to download build 15007:1000 but since 2 days.. It is not downloading.. Taking a lot of time to download. Pls help.. God bless u.