Is the mould like a white fur or are there black spots on the fabric. If there are black spots then the fibres could be damaged as the mould would have digested them if they are natural material like cotton.
If its just surface mould than a normal clean with Clensan, Formula 429 or Microkill in the tank and post sprayed will deal with it.
If there are black spots they can sometimes be reduced using coffee stain remover. Pre qualify with the customer first that you may not be able to remove them totally.