Return it.

Here are some settings you want to check:

Have both SSIDs (aka network names) the same with the same password. Let the device pick the stronger signal. 2.4ghz is slower but goes farther, 5ghz will be faster but the signal wont travel very far (physics).

Make sure you are using at least WPA2 level security with AES. Do not use AES TKIP, WPA or WEP. That should make the weak security banner go away.