IMO, you need to contact / visit the relevant excise and taxation office, for resolution of this issue.
I am quite hopeful that some details will be mentioned on relevant excise and taxation department website. Please check, and if you do not get answer to your query, then you may visit the office with relevant docs, all details, etc., and apply for change in vehicle's particulars. I think, some fees may be there for rectification of the issue.
Still, relevant excise and taxation office can guide you best in this regard.
I hope, it helps. Thank you.