How do I mark a To Do as done?

Mark a To Do as done from the Agenda

1.) To mark a To Do as done, swipe it to the left.

2.) Or Tap on the To Do and then tap on the checkmark to mark it as done. A filled checkmark means the To Do has been marked done. 

Tap on the bookmark icon to change the reminder date and time. 

Mark a To Do as done from a Profile

Tap on the To Do in the To Do section of the profile.