To edit an existing Check-in in Slack, navigate to Troopr home tab where you can see the list of all your Check-ins. Choose the Check-in, Click on "Other actions" ⇒ "Edit" to launch the Check-in editing form.
The form is the same as the one for creating the Standup and allows you to change any of the Standup attributes.
From the Wepapp: you will see the option under check-in setting;
Upon submitting the changes, you will get an acknowledgement message similar to creation acknowledgement. No messages will be sent to participants about the changes.