Use Airplane Mode

Using Airplane mode is a quick way to disable all your wireless connections, including your cellular data. When you turn Airplane Mode off again, your iPhone will start searching for the strongest signal available, and you should be able to connect to cellular again.

To enable Airplane mode on your iPhone, open your Control Center. If your iPhone has Face ID, swipe down from the top right corner of your screen. If your iPhone has a Home Button, swipe up from the bottom of your screen.

Once you open the Control Center, tap the Airplane mode button (the one that looks like an airplane) in the top left corner of your screen.

Next, wait a few seconds and turn off Airplane mode. Wait another few seconds, and then try using your data.