How to access the web interface of another subnet?

Question

Network routing

Hello, a question for network administrators. I'm not really into this.
There is a router to which the Internet is connected (X, Microtik) and behind it several routers with their own subnets (A, B, C, D ...). Since there is no direct access to the router, hence the question: is it possible to enter its Web panel? I read that it is necessary to correct the Gateway, etc. on the connected device, but so far without success.
On routers, the network configuration is approximately the following:
https://drive.google.com/file/d/1DI8M_smR9iGzLv521...

Answer 1

So which router do you need to get into? On Mikrotik? Its address is 192.168.88.1. Don `t come in? Doesn't ping? Are you sure that the web-muzzle is enabled on it? Are you sure it's http and not https? Have you tried Winbox to connect? What about SSH?

Answer 2

and who is stopping you from accessing the web interface of the router at 192.168.88.254?