Hi and thanks for the query.
There is a problem with occlusion. The retainer might have migrated and displaced from its intended position. Unfortunately, there is nothing you can do at home to fix this and you will need to see your Dentist for a more thorough evaluation. The dentist might have to readjust the position of the retainer or give you a new one.
Let me know if you have further questions.
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Wish you good health.