You can edit any activity, except email interactions, directly through the Activity timeline in any profile.
Select any profile and click on the Activity timeline, as shown below.
To edit an existing interaction simply click the pen icon on the right side next to any interaction to update timestamps, submission questions, donation amount, etc. Once you've edited that interaction, click the Save icon at the bottom of the page.
Please note that a form's questions and answers submissions cannot be edited. Changes will not be saved if you don't click the Save button before exiting.