Ethernet/IP communications with the SLC 5/05 can be complicated.
You first have to make sure the SLC is running FRN 10 or Higher. (You can find out what FRN version of the Processor you have by looking at the sticker on the backside of the unit before inserting it into the rack.)
Then you have to use the EEM instruction in the SLC for communications as this compiles the CIP packet transmit/receive for a specified IP address.
You can find more information on that side of it here.
Then on the Codesys side, you would need to purchase the ethernet/ip adapter module SL. You can find information on that configuration here.
If you just need a small amount of data, I would recommend using Ignition Edge onboard as that will save you quite a bit of time. You can find information on tag mapping across controllers in Ignition here.