How does one calculate how to dilute a solution to working strength?
Since its 6x (6 times concentrated), you have to dilute it 1:6, so you add 1ul of 6x dye for every 5ul of reaction.

5 +1=6ul final volume

6ul final volume / 6x concentrated = 1x working concentration

Now the dye is diluted down to a 1x(working) strength.