Forgive me if I'm over simplifying this for you. It just sounds like you need a primer. Start by downloading bitvise. It's an ssh client. Might as well download notepad++ because everyone should.

Use bitvise to login to your er-x, now open a terminal and type 'show configuration all > config.txt'

Go back to your bitvise client and open a ftp window. Download your config.txt and delete the file from the er-x. Sanitize as needed and post it here.

If you really want to manage your router effectively you'll want to be familiar with the command line interface.

When you swapped routers did you power cycle the modem? Some ISPs won't allow the hardware swap without the power cycle. I used to see this with Cox Cable modems a lot. Not sure if it's still a thing so ymmv on that one.