How do I text androids on an iPhone 7

Because you have no actual cell service as shown at the top of your screen shot.

You need cellular service to text Android devices, you cannot do so over Wi-Fi.

Contact your cellular service provider, and verify your service plan is active, and your SIM card is working.

You need to have an SMS plan enabled by your carrier for the SIM/eSIM that you use on your device. Apple Inc does not provide SMS services.