First, suggest discarding it, as it was never meant to be cleaned. It's a glorified doormat.
I was taken to court and lost, when a tech cleaned this stuff using HWE, even after the tech warned the client of shrinkage and the client accepted the risk verbally. The douchebag lied in court. The judge said if I knew it would cause damage, I shouldn't have cleaned it. I was knowingly negligent. I'm sure the tech was not that careful with his use of water.
Having said that-
Set the customer's expectations very low.
After the customer has released me of ALL responsibility and signed the paperwork.
I've had ok results using hydrogen peroxide over the entire surface and using HWE wisely.
I would think an OP machine with peroxide juice, such as
TOPS or
Saiger's would give good results.