To set an IP address, you need to know the "subnet" that is used by your router. Most home routers use either 192.168.1.x or 192.168.0.x, where x may be 1 through 254. Your router may use something other than 192.168.1 or 192.168.0, but the last set of numbers must be 1 through 254.
There are two steps to setting a static IP address.
First you need to inspect your router's configuration utility to determine the range of IP addresses that it uses for automatic allocation (the default when devices are connected). For example, this screen is from an old Linksys wireless router:
In this example, the subnet used by the router is 192.168.1.x. IP address 192.168.1.1. is used by the router itself. The router's DHCP server is configured to automatically allocate IP addresses from 192.168.1.100 through 192.168.1.149 to devices that are connected to the router. That means that you can configure a static IP address to be any of 192.168.1.2 through 192.168.1.99 and 192.168.1.150 through 192.168.1.254.
Some routers default to using the entire subnet as allocable addresses, e.g., 192.168.1.2 through 192.168.1.254 (.1 is used for the router itself and .255 is a special "broadcast" address). If your router's DHCP server is configured to use the entire subnet, you have to reconfigure it so that there will be some IP addresses that will never be allocated by the router's DHCP server. If you need help with this, look at the label on your router and provide its name, model, and hardware version (if any).
Once you know a valid IP address that will NOT be used by the router's DHCP server, you have to go to the printer/scanner configuration utility and set that IP address into the printer/scanner. How you do this depends on the device. You need to refer to the device's User Guide for instructions. If you need help doing that, identify the specific make and model of your device.