The red circle below is the part of the block that the bumper should clip straight into. If it doesn't, the little black clip in the block might be broken. You might need to get he bumper out of the way to check it properly. It might not be broken, there might just be something in the way preventing the clip engaging fully. If it is broken, you can replace the block, it's held on by two t25 torx screws circled in blue on the second image. The part number of the passenger side block is 7E0807183B.
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