How to use variable, which value should be set in keyword or test, in XPATH?

I need to click on element based on what value it contains..but I want to set this value in test run or keyword definition (best option is in the test I guess) How should I do it?

the variable containing xpath should look like that:

${DROPDOWN ITEMS}    xpath=//*[contains(@class,'listitem-element')]/span[contains(text(),'${second_number}')]

This locator works when I replace the variable with actual number like '002', but I want to have it more general..

In keyword definition I use it like:

Choose Value From Dropdown
     focus    ${DROPDOWN ITEMS}
     click element   ${DROPDOWN ITEMS}

and in test I just call the keyword

my question is where and how to set the variable value of ${second_number} variable used in xpath? PS:the xpath definition, keyword and test are each in separate files thank you!