In order to enable the iCloud sync in the app, please go to the settings of the app and make sure that the ‘iCloud Sync’ toggle is turned on under the ‘iCloud’ section.
If the iCloud sync still doesn’t work, please make sure that you have enabled it in the settings of your device by tapping on your name, then selecting the ‘iCloud’ option, then in the ‘Apps Using iCloud’ section tap on the ‘Show All’ button, look for Doneit and make sure that the toggle for it is turned on.