Power Query Function for Custom Column

Hi Community,

I need a Custom Column whereas

     Index Column=1 then Custom = 1,

     Index Column=2 then Custom = 2,

     Index Column=3 then Custom = 3,

     Index Column=4 then Custom = 1,

     Index Column=5 then Custom = 2,

      Index Column=6 then Custom = 3 and so on.
Please do favour if you would help me