2 modems routers on same LAN

[Victor_Wright]

My LAN is setup with a tplink TD-W8970 router 192.168.1.1 with DHCP and i have several pcs and laptops using this as the internet gateway.
Recently i have also acquired a 4g modem router with lan port which i need to connect to my LAN
It seems to have a built-in ip of 192.168.8.1 and DHCP can be disabled or configured.
How can i connect this 4g router to my LAN so that i can use that internet when the other internet is slow or select some PCs to access the internet from 4g instead of the tplink?

 

[bill001g]

It is not real standard but you could just disable the dhcp on the 4g router and hook the lan ports of your router together. If you want to use it your would manually set your end device with some ip in the 192.168.8.x range and set the gateway to 192.168.8.1