Not only to make it look more professional
First the dog is eight weeks and is taught obedience and socialization. Then when it’s 18 months the dog does a four-month training class. After the dog passes the dog gets to train with the blind person they matched with. Lastly this training can last between 27-20 days
I think the way to correct this preposition would be to remove the word "among" and swap it out for the word "between".
Also, it is true that a computers spelling tool finds every mistake in a document, like incorrectly spelled words and fragments and run-on sentences.
Hope this helps :)