A simple way to sweeten your mead is to put the Mead in the bottling bucket. Taste the mead and see if it is like you want. If so, then bottle - but If not,  then mix a sweetning mixture of Sugar and water or Honey and water.

Slowly add a small amount to the bottling bucket and mix well but do not aerate the mead - stir easily. Then re-taste and see how you like it now.

Continue this process until you get the correct sweetness that you want.

You will need to add Potassium Sorbate and  Sulfite (Campden Tablets) and mix in well. This should prevent any possible fermentation starting back. (Use the manufacturer recommended amount for the Sorbate and add 1 Campden Tablet per gallon of must) Put back in fermenter and sit in a cold place for a few days to a week.