That's a bummer man. The best thing to do is just to go back through the days you swam and change the units, hit the pace recalc button and resave...then your pace and totals should be updated.
Working from the calendar view may be easiest. Shouldn't take you more than a half hour
I did the same thing when I started swiming last spring. I was wondering why I was THAT much slower than before. It was a pretty good day when I found that out. I'm used to yards so I can't relate my times to previous times.