Need help port forwarding with two routers

Hello, there's a problem i'd like to solve in our company. I am no expert on networking so please bear with me.

I have the following infrastructure (simplified): https://imgur.com/OH40EBZ . We have 1 modem router provided by the ISP (we have to call them to change any setting) that is connected to another router of us, so we have two routers which is essentialy having 2 filters.

What I need to do is set up the port forwarding scheme with the ports in which the DVR works (8181, 554, 8000, and 1 more), to be able to access the web interface from the internet. Currently, you can use the interface with a device within the network and loading in the browser http://192.168.2.30:8181

I've read that setting a router in DMZ(or bridge) mode makes it easier to do this, but in the company they are not convinced about it, so i am trying to do the port forwarding with the 2 routers.

To what IPs should the rules in the first and second router point to in this case? I've tried pointing from public ip to 10.10.10.4 in the first router, and from 10.10.10.4 to 192.168.2.30 in the second router, but no results.

Thanks in advance.