I'm guessing some people were never taught manners by their parents, so I'll do it for them.
When sending a DM with grammar and typo corrections, it's polite to start the message with a greeting, something like "hello" or "hey"
Then you say something like "I'm enjoying your story, but I spotted a few typos..."
Then you sign off with, "keep up the good work," or simply "regards or "
Manners cost nothing and make the difference between me reading your message and fixing the errors if I have time, or simply deleting your message.
Regards
Alan