Good luck. I literally went through something similar a few weeks ago. It took a little time but my entire network runs better now. You got this!

You can avoid that by using the same Wi-Fi network name and password that your current network uses. Your devices won’t know the difference.

I just want to reiterate what others have said: do some googling about your router make and model. Look for the instructions for “hard reset” or “factory reset”. Follow those instructions. Once you do, you should be able to find the default login online.

Once you’re able to log into your router, I’d suggest keeping it as your DHCP server and simply following the instructions to set up a pihole with it. Everything seems to work more smoothly without the pihole as DHCP server.

Do you know if your router is acting as a DHCP server? Most do, and if you’ve set up the Pi as one without logging in and turning off your router’s, you’ve set up two conflicting DHCP servers, and that would explain your issues.