On Lego Harry Potter how do you get past the locked door after learning ridikulus?

You're likely referring to the locked door in the Forbidden Forest after learning the Riddikulus spell in Lego Harry Potter: Years 1-4.

Here's how you get past it:

1. Learn the Riddikulus spell: You'll encounter a Dementor in the Forbidden Forest and learn the spell from Professor Lupin.

2. Use Riddikulus on the Dementor: You'll need to aim your spell at the Dementor and cast Riddikulus to make it retreat.

3. The door will open: Once the Dementor is defeated, the door in the Forbidden Forest will open, allowing you to proceed.

Let me know if you have any other questions about Lego Harry Potter!