Hi jvnatale,
You cannot merge data from two different Apple ID's on your iPhone the way you propose.
If you need specific data from some apps that you want in your new device, I recommend to contact the app developer of those apps in order to see if the apps in question offer a way to do a backup of the data in order to restore it the new device.
When you set up your new iPhone XS, you should have seen an option to restore the iCloud backup of the iPhone 7 Plus to your new iPhone. You might still be able to do that.
Transfer content from your previous iOS device to your new iPhone, iPad, or iPod touch
Moving forward, use the same Apple ID on all of your devices and If you would prefer to use the Apple ID you just created instead of your old one, then, you might try copying and pasting the app data information on your iPhone 7 Plus into an email and sending it to yourself to open on your iPhone XS.
Take care.