If I am reading this correctly, you want some way to move a character into a locker upon activation of some kind?
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Find an animation to move said character into locker. “enter locker” or “locker transition” with “animation” and “fbx” searches on the Internet should pop up some results. Find a suitable one and import that into Unreal.
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Apply the animation to the character following one of the hundreds of animation tutorials available.
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Give the locker two reference points for navigation, the inside of the locker and the outside of the locker. The position of these points will vary depending on your locker, but generally the inside point is in the middle of the locker space and the outside one is about 100 units or so away from the closed door of the locker.
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Have the locker provide those two reference points to the character so that the character is in the correct location and rotation when starting and ending the animation for locker entry (animation file from step 1).
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Provide the character with the ability to activate this locker entry function, either through some kind of action mapping or mouse clicking or whatever you deem fit.
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Blind the character to the AI once the locker entry has completed.