Hello @nehaj,
I can’t tell you what what value Mode requires but can tell you how to find it out. To export node’s configuration as flow variable you need to write some string in the text field close to the drop-down menu in the row corresponding to the node configuration to export. This will create flow variable with given name and you’ll see what value Mode expect 
See here for more:
https://docs.knime.com/latest/analytics_platform_flow_control_guide/index.html#creating-local-flow-variables
Br,
Ivan