Hi, can’t find how to edit a too fast swim split/interval. Looks like this 
It might depend what went wrong.
But you can try loading the fit file into https://www.swimmingwatchtools.com/ and see if it is able to fix it.
Hi,
the incorrect rest intervals were not editable with that tool but I used FIT File Tools
to delete the “corrupt” section.
Pressing Garmins Lap-key too many times leads to incorrect data.
Thanks, Steve