Iphone 7 wifi problem.

My iphone wifi not working, when I go to wifi iphone can't find the router name in search.

When iphone restarts then wifi can connect to the internet router but only for 2 or 5 minutes then again loss the connection. Again going to the wifi in my iphone the name of router not visible again iphone need to be restart. Again Wi-Fi is just working for 2 or 5 minutes.

Please guide me for solutions of this problem.

Thanks

Zaki Ashna