A new phone is exciting right up until you remember everything currently living only on the old one. For a local POS, the fix is straightforward as long as it happens in the right order.
Step 1: back up before you touch the old device
Go to Settings on the old device and download a full backup while everything is still there and working. This should happen before any factory reset, trade-in, or "just in case" cleanup of the old phone.
Step 2: get the backup file onto the new device
Email it to yourself, use a cloud drive, or transfer it directly via cable — any method that gets the file physically present on the new device works fine.
Step 3: set up fresh, then restore
Open the tool on the new device, complete the very short setup (it takes a minute either way), then use Settings → Restore From Backup and select the file. This replaces the freshly-created data with everything from the backup.
Step 4: verify before relying on it
Check that your product list looks complete and a couple of recent sales appear correctly in the history before treating the new device as fully set up — catching a problem here costs a minute, catching it after a week of new sales is much messier.
Don't wipe the old device until you've confirmed the new one works
Keep the old device untouched (or at least keep its backup file) until you're confident the new setup is solid — a safety margin that costs nothing and prevents a genuinely bad day if something didn't transfer correctly.