Question about TP-Link Archer AX50

Hello everyone, I bought this router because of the many good reviews. Now I have to find out that the router is not found via thether app. I operate the router behind a cable modem. now I have tried to access the router via the web interface via network cable (internet works there). however, it tells me I have the wrong password. I then tried to reset the rvia hardware, but the router just won't reset. does anyone have any tips on how I can solve this, otherwise I'll probably have to send it back. I also wonder if they sent me some returned goods and that's why the password doesn't work. all in all, very unsatisfactory.