If you have a 1SE Pro subscription, use 1SE Cloud Backup instead—it's the backup we can check and restore for you. The steps below make an iCloud backup of your iPhone, which works without Pro.
Back Up Your iPhone to iCloud
Make sure 1SE is included in your iCloud backup by following these steps:
Ensure your iPhone is fully charged and connected to Wi-Fi.
Go to Settings > [your name] > iCloud.
Tap iCloud Backup and make sure Back Up This iPhone is turned on.
Under ALL DEVICE BACKUPS, tap "This iPhone" and check that 1SE is turned on in the apps list.
Return to the previous screen and tap Back Up Now.
Stay connected to Wi-Fi until the backup finishes. When it's done, the date and time of your last backup appear under Back Up Now, and that backup includes 1SE. If Back Up Now won't start, check Wi-Fi and your free iCloud storage.
If you'd like a more detailed step-by-step on how to back up with iCloud, check out Apple's help article.
Important: signing into iCloud on your new iPhone isn't the same as an iCloud backup. 1SE isn't stored in your iCloud account; only basic data like notes, mail, and contacts are. To move 1SE, you need an iCloud backup or a computer backup.
Ready to move? Follow How to Move 1SE to a New iPhone Using iCloud.