Wi-fi said weak security how to fix

Change the security settings on your router to WPA3 or to WPA2 AES. How you do that varies by router. If you don't have the instructions for your router, do an internet search for instructions for your router brand/model or if your router is supplied by your internet service provider, check their website or customer support. Also see: Recommended settings for Wi-Fi routers and access points - Apple Support

Most older routers support WPA2 AES and that will discontinue the weak security warning. If you want WPA3 and your router doesn't offer that option you would need to buy a new router that does.

Feel free to reply with any questions and I or someone here will try to help.