I have a situation that I don't know how to resolve.

I have a Mikrotik RB750GL Mini-Router that sits connected to my WAN, and has one LAN port connected to a Netgear wireless router.

The Mikrotik is on the 192.168.88.x subnet, while the Netgear wireless router is on the 192.168.1.1 subnet.

A device that is connected to the Netgear router can ping a device that is connected to the Mikrotik router.

Any device that is connected to the Mikrotik router cannot reach devices on the Netgear router. Using ping, I get a Destination net unreachable. Using traceroute I see that the device on the Mikrotik router gets to the router, but then the next hop is outside in the Internet.

I'm sure that I need to add something to the routing table in the Mikrotik, but I am not familar with the web interface and need help with this. Any suggestions?

This is good, it does not work because they are behind a NAT

Where do I make modifications to the NAT to allow one subnet to see the other?

Where do I make modifications to the NAT to allow one subnet to see the other?

You need to turn NAT and the firewall off on the Netgear router. You then need to add a route to network 192.168.1.1/24 with the gateway address of the WAN address of the Netgear to the Mikrotik.

Alternative.
Turn off DHCP on the Netgear.
Connect port 5 of the Mikrotik to a LAN port of the Netgear.
Remove the slave setting on the Mikrotik port 5.
Add address 192.168.1.254 to port 5.
Add DHCP pool Netgear with address 192.168.1.10 - 192.168.1.50 to the Mikrotik
Add DHCP server to port 5 network with pool Netgear
Now the Mikrotik is doing the routing and the Netgear is just a switch and wireless AP.