To address this problem, go directly to your printer (Not your PC), select the network settings for wireless, then select your new modem/router from the list available and connect to it.
My name is Robert ***, I will help you too the best of my ability. Without a Make and Model doesn't give us much too go on, since you said that this is wireless it's set too use with the previous and needs too be set too use with this one. Sometimes, these unit's also, have a RJ45 connection which, you can run a patch cable in and connect too the Router/Modem and will issue a correct/new IP. It is also, likely that it is being issued else where and causing, a conflict with another device.