How to convert a criminal judgment of forging the attestation stamp of a document?

I have been convicted of a criminal case for documents, as I was unaware that the stamp attested on such documents was not original. It was done by one of my friends.

The court has given the judgment as 3 months punishment in prison. could you please help me with this problem?

Please advise, can I get the sentence converted to fine as well?

What am I supposed to do in this situation?