Replace or Dry the Silica Gel
1/ Lift the cover of the instrument and loosen and remove the silica gel holder by loosening the three plastic nuts. If possible cover the aperture to minimise moist air ingress.
2/ Place the holder into an oven for at least 2 hours at 100 to 200°C alternatively empty into a glass beaker, microwave for 5 minutes and allow to cool (Note: silica gel gets very hot, handle with care) and refill silica gel holder or replace with new fresh silica gel.
3/ Before re-assembling, let the silica gel cool down in a dry place to prevent damage of the optics. Let the instrument stabilize for 2-4 hours. Check your calibrations afterwards.