The tax return for the year you moved here is a different form

If you lived in the Netherlands for only part of a year, because you moved here or left, you file an M return for that year instead of the normal one. It is the return that settles that split year, and settling it is how any tax you overpaid comes back to you. You can file it online through Mijn Belastingdienst, or ask for the paper M form. Past years can still be filed.