To complete this objective, please make sure of the following:
Remove all the corrupted honey swirls ("the mess") from inside Pooh's House. Walk through each room carefully, as swirls can sometimes be tucked into corners or behind furniture and are easy to miss.
Pick up the hidden Box of Colorful Crayons from the floor inside the house. This item can be easy to overlook, but picking it up is required to trigger completion of the objective.
Once both the honey swirls have been cleared and the Box of Colorful Crayons has been collected, the quest step should progress automatically. If you've done both of these and the step still doesn't advance, please try exiting and re-entering the house, or reloading your save, and check again.