If you have a Pro subscription and backed up with 1SE Cloud Backup, see How to Restore from a 1SE Backup. Otherwise, you need a device backup that contains 1SE.
For iOS devices, immediately check for a backup that contains 1SE — in iCloud, or on a computer via Finder (macOS) or the Apple Devices app (Windows). You'll need to restore from this backup. Go to Settings > [your name] > iCloud > iCloud Backup to find a backup with 1SE.
Signing in to iCloud isn't the same as a backup: 1SE isn't saved in your iCloud account, only basic data such as notes, mail and contacts. You need a device backup, made to iCloud or to a computer.
iCloud backups
On your iPhone or iPad, go to Settings > [your name] > iCloud.
Tap iCloud Backup. You'll see the devices with iCloud Backup turned on.
Tap your device's name, then check whether 1SE is enabled.
How to restore from iCloud
For the full steps, see How to Restore 1SE with iCloud.