Sales invoice failed to submit

Sir, 

During 2008-09 period a sales invoice omited to submit to sales Tax. It was a capital good eligible for ITC with a Concession rate of % (by C Form). But we neighter submited to sales tax nor issued C Form to that party. 

Can I issue C Form in mannual form now? or Shoul I pay the CST concession received back by credit note?

Thanking you advance..