help my 2001 tdi octavia crank pulley has siezed

Hi hope someone can help. My skoda made a thud and battery light came on, the auxiliary belt had come off. Anyway I drove it as had no choice for another 1.5 hrs. Got home to find the big bottom pulley on side engine will not turn at all. All others seem fine. Is this simple to replace? I think another problem may be putting belt on once pulley replaced. Its a 2001 110 tdi

Thanks

Jon