How do I backup my iCloud without WiFi

Sorry, that isn't supported with an iPhone7 (only with the iPhone SE 3rd generation, 12, 13 models). See the following from Back up iPhone - Apple Support

Note: On models that support 5G, your carrier may give you the option to back up iPhone using your cellular network. Go to Settings > [your name] > iCloud > iCloud Backup, then turn on or off Backup Over Cellular.

You can backup to a computer without using wi-fi.