How do I correct the amount of Ok State Tax withheld

You have to fix it on the federal side where you entered the W2 or 1099.  W2 box 17 or 1099 box 14.  Then click on the State tab to start the state over for it to update.

Or have you already filed?

I already filed but Ok wanted a copy of my 1099.  As I was checking over it I realized I inadvertently typed in the amount withheld from my Fed tax not my OK tax.  I don't know whether to try to fix it prior to sending them the 1099 or to send it then file an amended return then return the overage they will have sent to me.