I THINK MERELY WRITING A LETTER FOR CHANGE OF SPELLING IS NOT ENOUGH. TECHNICALLY IT IS A CHANGE IN A LEGAL DOCUMENT AND THREFORE IT HAS TO BE DONE THROUGH LEGAL PROCESS ONLY.
IT WILL BE ADVISABLE TO SEND AN AFFIDEVIT SIGNED BY APPROPRIATE LEGAL AUTHORITY LIKE MAGISTRATE OT NOTARY PUBLIC , MENTIONING THE GENUIN MISTAKE IN ONE OF THE DOCUMENTS.
REGARDS.
KKD