Hey droidsoon,
"Reset Network Settings" will reset Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that have been saved on your iPhone. This will not affect your other data.
Please note, however, that the "Erase All Content and Settings" option WILL remove your data from the iPhone.
Reset your Network Settings. Tap Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before.
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
https://support.apple.com/en-us/HT204051
Cheers,
Allen