Cloud Cuckoo Land
On the small round spinning platform to the right there will be three pictures with three buttons to step on. Match the spinning blocks with the pictures in the background and the Red Brick will appear.
For this you need to light 3 fire plates to ignite fireworks. They can be found to the far right platform where you need to hop across the flying plane, to the far left, through the rainbow to the second floating platform, and right beside the entrance, to the left there is a tower with rainbow pieces in front of it. Break them with Unikitty and then climb up to find the fire plate there to ignite and receive the Red Brick on the lower level.
Fast Secret Knock
Go through the silver door on the left after destroying it and use a master builder to put the three pieces together. Climb up the stairs and use a female character to cross the rope to enter the tower and find the Red Brick.
Look for the three purple and white boxes in the area that you will need to use a construction worker on. There’s one directly in front of you to the right when you enter and go down the stairs, one through the silver door on the left and one in the tower to the far right. Wrench all three and the Red Brick will appear beside the construction station.
Red Brick Detector
Find all three instruction pages; between the custom Lego character builder entrance and the silver door on the left, there is a pink and blue bar to jump up to. Grab it and pull yourself up to find the page there. The second is on the small island where the three spinning pictures are. Use the grapple point on the tower to open a door and go through or just fly up to the top, to find the instruction in the hole in the centre.
For the final page, go through the silver door on the left and master build the three pieces to build a staircase. Go up and cross the rope to find it in the tower where the Fast Secret Knock red brick is. Now use the construction station and once the Merry-Go-Round is built, the Red Brick will appear.