I have a printer which is connected by Ethernet port. When I turn on the printer, it has some default IP address (not on my network). I can't print documents, as it says printer is off-line. I have to unplug the printer network cable from the router, and then re-connect it, and it then picks a valid IP address.
I contacted the printer company, who said, I can give my printer a static IP address. However, how can I do the same on the router, so they both have the IP address? (Or can I get away without doing anything on router?).
Not knowing which router you have, I can only give general advice.
On one of the settings pages, there should be settings for the IP range assigned by the router. Further down the page there is usually somewhere you can add a list of reserved IP addresses. Add your printer name, IP address, and MAC address there.