VTK output for user-defined variables of particles

Dear all,
I wish to output VTK variables for particles.
I recognize that a keyword named ‘vtk_part_usr_var(,)’ can do such work.
First, I fail to find the area which can activate this keyword in the GUI
Second, I try to add the keyword ‘vtk_part_usr_var(1,1)=.True.’ artificially in the data file but it does not work
Does anyone know about this? I appreciate a lot!

Hi, I have resolved this and there is another keyword ‘des_usr_var_size’ need to be specified
Kind regards