how to connect to other wifi

See -> Recommended settings for Wi-Fi routers and access points

Recommended settings for Wi-Fi routers and access points - Apple Support

If you need help with your Wi‑Fi password

If you need help with your Wi‑Fi password - Apple Support

Update your iPhone to iOS  iOS 16.3.

This warning is basically telling you that the Wi-Fi network you are trying to connect your iPhone to is not secure. It is either using a "weak" wireless security method or none at all.

If this is your home's network, you will need to adjust its wireless security settings so that it is using WPA2 with AES, as a minimum. If your router does not support that, you have, at least, two options:

1. Continue to use this router's wireless network, knowing that it potentially can be compromised, or
2. Replace the router with a newer model that supports this setting, and better yet, will support WPA3.

If your network you need a lot more security at the router end

if not, forget that network. Then join a trusted network using WPA2 or 3