There are different means to attach the candles, but I'm going to use floral clay. It is strong, holds tight, won't come loose if gotten wet and comes cleanly off the glass and pedestals if I wish to use them for a different event in the future.
I do NOT recommend hot or cold melt glue. It has a way of becoming brittle (especially if refrigerated) and popping apart at the most inopportune time. Heating up a glue gun to reattach at the reception hall is a BIG PAIN!
A roll of floral clay is handy for SOOOOOOO many uses! I never go to a receptional hall without a roll in my box.
Make sure the glass is clean and free of oils. Allow to air dry if you wash the votive cups.
Put a small rolled ball in the center of the pedestal cap. Push down hard with the votive cup to spead and attach the glass firmly to the top. The floral clay also comes in white if you prefer.
Here's a view from the bottom. This stuff holds fast with no drying time. You can take it apart - but it is a pain on site - so center the clay and don't use so much it squishes over the sides!