It sounds like you have two subnets. One is the regular one created by your ISP's router. The other is created by your wifi router. In other words, you have a cable from your ISP router is going into the wifi router's WAN port.
If this is correct, then you want to combine the two subnets into one. That's relatively straightforward, but is a little tricky to get it right.
1. Login to your ISP router. Look at the DHCP allocation table. Make sure the range of DHCP IP addresses it hands out is 192.168.2.100 or higher. That is, it should never assign an IP address in the 192.168.2.1-99 range via DHCP. Save the new settings.
2. Configure your wifi router.
2a. Unplug your wifi router from the ISP router. Cover the WAN port with a piece of tape so you don't accidentally use it again.
2b. Change your wifi router's IP address to a static address of 192.168.2.2.
2c. Disable your wifi router's DHCP server.
2d. Plug the cable from the ISP router into one of the wifi router's LAN ports.
2e. (If you mess this up, you will be unable to login to the wifi router again because DHCP is disabled. You'll have to reset the router, reboot, and try again.)
Reboot the wifi router. Any computers connected to the wifi router should be reconnected or rebooted.
If you did it properly, the wifi router is now just an access point on your ISP router's network. You can access it via 192.168.2.2, just like you can access the ISP router via 192.168.2.1. The ISP router is handling all DHCP requests, while the wifi router is ignoring DHCP requests. And devices which connect to your wifi router will be visible on the ISP router's network (and vice versa).