Is there a way to fix several time entries at once instead of one by one?

Yes — Kliently supports bulk edit. Select multiple entries and change them together instead of opening each one. It's the fast way to clean up a week before you bill it.

Common uses: reassign a batch of entries to the right project after you tracked them under the wrong one, or flip a group of entries from non-billable to billable (or back) once you've decided what's actually chargeable. Filter the view down to what you want to change, then edit the selection in one move.