How to freeze & reheat quiche

I'd recommend letting it cool to near room-temperature, then place it in an airtight sealed plastic freezer bag before it dries out too much. You can spoon some of the juices from cooking into the bag with the steak so that when it defrosts again the juices will be in there working to keep it moist.

When you defrost it, do so in your fridge leaving it overnight so that it defrosts gradually, keeping it in the freezer bag so it doesn't lose any more moisture. It should then be good to reheat, probably best in a shallow pan rather than a microwave to retain moisture.

It sounds like you've forgotten (or not been directed) to blind-bake the crust. Blind-baking is baking a crust without a filling so that it gets a head start, sealing it and preventing it going soggy.

To blind-bake, place the pastry in the dish as usual, dot the base with a fork in a few places, then cut a square of baking paper roughly the same size as the dish, place it on the pastry, and add some baking weights (small ceramic balls) or dry kidney beans. These stop the pastry from bubbling up.

Place in a pre-heated oven for about 20 minutes until the crust is lightly golden. Remove from the oven, remove the weights and paper (if using kidney beans, you can use them again, but don't cook them to eat!) and let the crust cool for 30 minutes before adding the filling and completing the baking process.