I have an issue with the PIE version of MIUI 10.2.1 PEDMIXM.

I suspect PIE is causing my phone's Toggle (Singapore) app to hang while video is casted to TV.

Since before updating to the latest version of MIUI, Toggle does not have any issues at all.

So how do I go about downgrading to Oreo?

I know where to get the file MIUI 10.2.1 Oreo, just unsure how I can downgrade or rollback to OREO?