The thumbwheel is a special setting method on the 1794-AENT and 1734-AENT.
When you set the thumbwheel to any value between 1 and 254, the module uses the common Class C private subnet "192.168.1.xxx", with a 24-bit Subnet Mask of 255.255.255.0. This is the only network number that the module will use when the thumbwheel is set between 1 and 254, and you will get an "object state error" if you attempt to change the address to anything else.
To set the module to another network number (192.168.0.xxx" you must use the BOOTP mechanism and a BOOTP/DHCP Server like the utility that is included with RSLinx Classic. Set the thumbwheel for "999" to make the module use BOOTP.
Set up your PC for 192.168.0.xxx, configure the BOOTP/DHCP Server Utility with network parameters you want (usually subnet mask 255.255.255.0 and default gateway 192.168.0.1) and power cycle the 1794-AENT.
Once you have used the BOOTP/DHCP Server Utility to send the module an IP address, you have to disable BOOTP and DHCP either using the Utility or using RSLinx Classic.
The EtherNet/IP Modules in RSLogix 5000 Control Systems user manual has a very good description of how the thumbwheel-equipped adapters (1734-AENT and 1794-AENT/B, so far) work. It's a very useful manual when you're setting up EtherNet/IP networks. Download it (Publication ENET-UM001) from the literature.rockwellautomation.com website.