The fans are quite easy to replace on their own. Review this IFIXIT teardown [guide|73395] The 13” is exactly the same setup up. Jump to Step 11. You do need to take the logic board out to get to the fans screws.
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Why do you think you need to replace either one of them? Often times dust and debris cake up the fan blades which if cleaned solves the issue.
The fans are quite easy to replace on their own. Review this IFIXIT teardown [guide|73395] The 13” is exactly the same setup up. Jump to Step 11. You do need to take the logic board out to get to the fans screws.