Variable Declaration and Initialization in Robot Framework within a Test Cases block

You need to use the Set Variable Keyword to assign values to Variables outside the Variable Header:

*** Test Cases ***
Test Case 1
    ${item}    Set Variable    ${0}    #${}

    ${item}    Set Variable    ${true}    #${}

    ${item}    Set Variable    Stackoverflow

The above assigns the variable you have given in your test cases to the correct value. (This will overwrite ${item} every time of course however) But this will assign the value, to the var ${item}.

Read the Docs about it here

Any questions please ask :)