What do I need to remove the plastic casing to attach the pedal cover?

Anyone

http://www.briskoda.net/forums/topic/206361-how-do-i-fit-a-fabia-vrs-footrest/page__hl__+footrest#entry3057627

if you mean the alloy covers on the throttle brake and clutch they just pull off its rubber that folds round the pedal

if you mean the foot rest to the left of the clutch theres a plastic 13mm nut at the top of it ......

you undo the nut pull it forwards so it clears the threads then it goes upwards i seem to remember ??

Yea I took mine out to fit the footrest. It made the job x100 easier.

if its a vRS alloy cover on the foot rest there's no need to remove it just screw three self tappers into it.