Routers are also gateways so they will usually have an IP. For example, it will usually end with .1 or .254 of the subnet (like 192.168.0.1 or 192.168.0.254).
The router should have an Ethernet port so if you set your laptop/computer to connect via ethernet (i.e. switch off wifi), set network connection to be automatic via DHCP, connect the laptop to the router with a cable, then you can see what IP address is allocated. (for windows try "ipconfig /all" and for unix variants use ifconfig -a)
Based on that gateway IP, you can go to http://<gateway_ip> or to https://<gateway_ip> and you should see a login page to the router. Try the admin password on the back (which is usually different from the wifi password) and then you can reset the wifi password.
Also look at this to see if that helps :
https://setuprouter.com/router/huawei/hg8145v5/v5r019c00s105-globe/login.htm
If you are trying to extend coverage by having a second router, it is more of a headache unless said router has a Access Point mode. ISP-provided ones are generally modem-routers so will not have that mode enabled