When storing apple crumble you should cover the apple crumble with some plastic wrap.
Then after covering the apple crumble with plastic wrap you should place the covered apple crumble in the refrigerator to store it.
The apple crumble will last in the refrigerator for up to 3 days before it starts to go bad.
If you've left the apple crumble in the refrigerator longer than 3 days then it may be bad and probably should be thrown out.
Look at the apple crumble and if there is any mold or bad smell to it then it has gone bad and should be thrown out.
You can also store your apple crumble in the freezer to make it last a bit longer.
Just wrap the apple crumble in plastic as well and then place the apple crumble in the freezer and the frozen apple crumble should last for 3 months.
But the apple crumble is better tasting and stays fresher when refrigerated and not frozen.