I recently set up time sheet entries for a date range & picked the wrong "issue". I've been directed to change it, but I can only do so day by day and I'm changing 3 months. There has to be a better way as this is slow, boring, and error prone (because it's so boring). Did I say it was boring? ;-)
You (or someone in your organisation) should have permission to do this. You go to reports and look at you time logged, then choose the 3 dot icon next to the filters and "Bulk edit" then under select action choose "Move"