Moin, Research and read up on what others have done to get past this type of problem and you should be successful in getting your router back to a factory default state;
https://www.snbforums.com/search/?type=post
If you follow the recovery steps written in the Wiki, you should be able to restore/recover using the Asus recovery tool. You're in a place where many others have found themselves so don't give up. Some have reported that keeping the WPS button depressed longer than the usual 5 seconds during boot up, after leaving the router unplugged for a few minutes helps; again, read what works for others. Without knowing your familiarity with the RT-AC3200 FW or your level of expertise working with different FW, it's difficult to pin down or diagnose the problem.
The following is only a suggestion, but part of a routine we've used successfully, but it's not carved in stone, so the YMMV rule applies. While you're trying to get the router to factory default, keep it unplugged from your modem and removed from WiFi internet access of any kind. Use a known good (or new) Ethernet cable connected between your computer plugged the router (port 1 or 4 as long as you know either port is working). If you use a laptop, be sure the WiFi and Bluetooth is turned off then bring up a fresh browser session when you log in the GUI each time and/or following a reboot, or after you've removed power from the router. Sometimes unplugging power instead of doing a regular reboot helps whatever you've applied to settle in, again, YMMV. After applying FW, logging out and powering down, just wait it out.. Taking screen-grabs of each step you've completed can be helpful for others to help you trouble-shoot, and can be easier than writing it down. It helps you to know what you've completed and what steps do or don't work.
After you've successfully recovered the FW, set the ID/PW and the router's IP address to the address that you want, save, then save, reboot and from there you can allow the router to connect to the modem/internet to finish your setup. Upgrading, moving between and/or reverting FW versions can become tedious. Get the router set up and stable before allowing it to phone home. Researching the site can take a while, but it will help you get a better feel all of this. Good luck. S.