I Bought a RAk7289C.
At channel plan i am trying to select region EU868, but it is not available.
Looks like you bought the wrong gateway.
The RAK7289 is available in different hardware versions, if you bought a RAK7289 for US915/AU915/KR920/AS923, it can be used only for these regions because the concentrators are different for other regions. That’s why 8xxMHz can not be selected on a RAK7289 for the US915/… bands.