You can change a due date on a post under certain circumstances:
If you created the original post.
If you added assignees to someone else’s post, you can edit the due date for those assignees.
If someone from your company created the post and assigned it to a company or a person outside of your company.
You can only change your own due date if you assigned the post to yourself.
On your mobile device
Tap into the post to get started.
Tap on the orange Assign button on the bottom left hand corner.
Tap the top due date to change the due date for the entire post, or the due date next to a specific assignee.
Choose Edit Due Date (choose Delete to remove the due date completely).
Choose the new due date and tap Set.
Click Update from the top right.
On the web
The process is very similar on the web.
Click into the post and choose Update assignees from the bottom left.
Click on the relevant due date to update the date or click on the x to delete it entirely.
Click Update to save the change.