Open Settings
Tap Cellular or Mobile Data
Tap Cellular Data Options
Tap Voice & Data
Select 5G Auto, 5G On, or 5G Standalone if available
Make sure your carrier supports 5G
Make sure your iPhone model supports 5G
Make sure your SIM or eSIM is 5G-ready
Turn on Airplane Mode and turn it off again if 5G does not appear
Restart your iPhone if needed
Update iOS to the latest version if needed