Here is what I did to make it visible again. I’m new so my influence is very little.
Identify who flagged you. Take the URL of your flagged post, replace the “it” in “Steemit” with a “d”. So your URL will read “https://steemd.com/……”. You’ll see who flagged you on this new page.
Contact the person who flagged you. If they’ve also commented and it seems appropriate, reply to their comment. If it makes more sense to message them privately, use this tutorial. . . However you attempt to connect, be polite- no sense making things worse. Ask if you’ve done something wrong and if you’re willing offer to adapt the content if they’ll remove the downvote. Try a couple times if it helps. Don't take it personally. Downvoting is a part of the process where the community self curates the content it likes. At this point its just not perfect.
Verify that the person who flagged you is active on the site. Give it a couple days, check their activity to make sure they’re not just away if you haven’t got a response yet. On the Steemd data page from your post, click their name and it will take you to a page showing their most recent activity.
Write a post about how you need help and your post is hidden. Leave a link to the hidden post. The intent of Steemit is not to remove valid original content that breaks no rules. You may get lucky and an influential person who feels bad for your plight will follow your link and upvote your post to counter the downvote and make it visible again.
Promote to get more viewers and upvotes. At the bottom of all posts there is a “promote” button. If you’re new you will probably need to buy SBD to do this. On your wallet page where you see your balances, click your balance for Steem Dollars, you’ll see a link to buy in the list. Follow the instructions and buy SBD with BTC to promote your posts. Please note: DO NOT PROMOTE A HIDDEN POST. Hidden posts will not show up in the promoted content list so your promotion will have no effect at all. You can promote the post that is pleading for help and linking to it however. You can also promote the hidden post once it becomes visible to help keep it staying visible. I had limited success using the promotion tool, but if you don't mind spending the money it may be worth trying.
Use @Randowhale to upvote yourself. You send them 2SBD and your link, they are influential and upvote your post. This is what finally worked for me. The Randowhale vote was influential enough to counter the downvote and made my post visible again. There are probably other paid services doing the same thing. Not pretty, but better than abandoning your work forever if you care about it.
Adapt your post and try again on a new post. I didn’t get to this point, but if Randowhale failed that was next. Try to figure out what made it draw a downvote in the first place and avoid that with the new release. Don't just re-post it exactly the same though, then you're spamming. . .
Purchase Steem Power to increase your influence on your future posts (also under wallets). After buying influence your own upvote will be more difficult to overcome with a downvote. Upvote all your own posts when you post them to help them stay on the positive side.
Of course all of this is dependent on your post actually being worthy of staying visible. If more people view it and don’t like it, you may be in trouble. Good luck! So far mine is still above water for now! haha
Here is the mediocre post I spent all this time addressing and saving.
And my pleading link to try and find help.
I’d love to hear ideas on how else to go about this. As I said, I’m new, this is just what worked for me.
Some guy just flagged all of mine, I called him out for stealing other peoples content.