Taken from the FAQ,
Q: Is there a way I can edit my logbook entry? After I checked my logbook submission and then hit the submit button, I realised I entered a callsign incorrectly.
A: Unfortunately there is no simple way to correct part of an entry. In the case of a Chaser entry you will have to delete the contact and re-enter it correctly. In the case of an Activator log it is best to copy the log of the activation and correct the copy, then delete the original and replace it with the corrected copy.
I’ve tried this and when trying to upload the corrected CSV file I just get this error,
An error has occurred whilst processing line 1 of the input file.
The error was:
Too few data fields. There must be at least 7 fields.
Please ensure the input file is valid SOTA CSV or TSV file.
I deleted the original log so looks like I will have to type it all in again.