、。
If by any chance you change your mind, please let me know.
Literal
By-chance thought [object-を] change-thing [subject-が] exist-[conditional-たら], me [to-に] inform-[polite request-て下さい].
考えを変えることがあったら is a layered hypothetical: 考えを変える (change one's mind) → 変えること (the act of changing) → ことがあったら (if such a thing should happen). The pattern [verb]ことがある means 'there is the occurrence of X,' i.e., 'X happens (sometimes).' Adding たら softens the condition to an unlikely possibility.