First, you need to enable the Check-in App and add your Team Members to it. You could do that by following the article How to Enable the Check-in App.
If you are previously using another time tracking app and will be switching to Check-in App, please follow the below steps after doing the instructions in the above-mentioned article.
STEP 1: On your RemoteTeam dashboard, click on People.
STEP 2: Click the Details button of the team member that you would like to assign the Check-in App to.
STEP 3: Click on Time Tracking.
STEP 4: Click the Settings button on top.
STEP 5: Select Check-In App under "Team member will use an app", then click the Save button.
User is now set to use Check-In App for time tracking.