900D broken hydro fan help please

[Sawtooth]

So every year or two a stick gets up under my machine and somehow finds it way to the fans on the hydro. I bought a new fan, but I am unable to access the nut that holds the original in place. Could anybody help me on the proper procedure to do this? My two current issues are access and when I do turn the nut how the fan turns also so I need to secure the drive system somehow. Thank you