After restoring the factory settings, you can use a computer with an Ethernet port to connect directly to the LAN port of the router with an Ethernet cable, open a browser and access default IP address: 192.168.8.1
Then you can access the AX1800 router's management page.
If you're connected via WiFi, the WiFi password/key is usually located on a sticker on the bottom of the router.
Once you're connected to the management page, please provide a screenshot of the Internet page to confirm that the router is connecting to the ISP's network.