How to make an insecure Wi-Fi to secure wifi

This is NOT an iPhone problem; it is a problem with your router settings.

A "Weak Security" notification means that your Wi-Fi router is not configured correctly. There is a new feature in iOS 14 that checks and displays a message if your router is not using the most up-to-date security settings. Note that your router has always had weak security, you just didn’t know about it until now. 

See this Apple support article for how to configure it correctly—>Recommended settings for Wi-Fi routers and access points - Apple Support, specifically the section headed Security. And don't forget to configure your range extenders (if any) also!

Note also that weak security does not interfere with using Wi-Fi, it is just a warning. Your Wi-Fi should still work normally, and, if it doesn’t, it is not because of the weak security message.

You need to get the manual for the router and follow it’s instructions to log into it’s control center, then change the security setting to WPA2(AES). It will be a selection on a drop down menu.

Change the security protocol on your router.