I was going through a friend's tagged pictures and accidentally tagged another of our mutual friends in it. How do I remove the tag? (The picture was uploaded by someone who isn't a friend.)
There's no option to remove a tag of your friend you requested on others photo but however you can remove your own tag.
If you tag yourself or your friend in somebody else's album, they are sent a request to accept the tag and its on them to accept or the reject the tag.
And if you want the tag to be removed, try to message the person who uploaded the photo and ask him to remove the tag. That's all you can do on your side.
The picture you are getting accidentally tagged or requested to tag yourself. You have to open the same picture on laptop, cause on Android mobile we can not have an option available or might be its getting lost. However on laptop you have to click on the same picture. On the right hand side you will see your name. Don't click on your name as it will turn into your Facebook profile page. Click on the side arrow and there you got it option for removing your tag is available.