Try to let them dry off to shrivel leaf. Once ready, I pull them and arrange on a barrow sieve on 5 gallon drums, well clear of the ground, for ,hopefully ,a sunny fortnight.It matters not if they get the odd shower but check that they are soil-free around the roots. Once dry, I clean the outer skins off, and any remaining stem/roots and store in mushroom trays in a ventilated covered rack against the north wall of the house.Generally good till Easter.Inspect as using and select and retain sufficient to replant next season.
Have found that the Brown shallots from supermarkets are a viable source of new sets but need soaking before planting to wash off any growth inhibitor