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The printer configuration that is loaded now has nothing to do with your current configuration.
I advice you to reinstall your printer anew... to suit the new modem/network. After deleting the current configuration, to avoid future confusion.
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I can help you through the difficult parts.
Is your printer a wireless printer, or a wired-by-USB-cable printer?
(It's almost certainly wireless, at this point... but it could be otherwise. )
The next step is simple. For the printer to be located, by wireless, for a wireless connection, it must be connected to the wireless network you have.
You will have to go into the printer's own panel, and its Wireless Settings (perhaps under 'Network Settings') and connect it to the present modem, simply. (It is not being 'found' because it is trying/configured to connect to the old modem/network. When connected to the current modem/network, it will be 'found', installing will proceed, and there you will be.)