If you don’t press backspace, the question will come back at the end of the review session, so I personally don’t use it unless it’s a typo(aka I typed too fast and my fingers got it wrong but I was thinking the correct answer)
I think its best not to rely on it too much, if you don’t know it well enough to get it right it’s better to just get it wrong so you can get lots of reviews and practice for it!
Some people backspace if the thing they got wrong was the word rather than the grammer but it’s up to you^^
Theres also something called a ghost review, which was something I was confused about when I first started so I’ll explain. There’s different settings but the default is when you get an example sentance wrong twice or more in one review session, a ghost appears on that example sentance. The ghost comes back and haunts you whenever you are reviewing(i’m actually not sure how frequently tbh), and each time you get it wrong(twice maybe?) more ghosts appear for you to fight. When you get it right, you vanquish a ghost, and ya gotta keep doing than until they are all gone, then that example sentance will appear normally again.
Some people don’t like these and turn them off, but I think they are good cause it means you’re practicing the stuff you’re bad at.
I personally would mark that us incorrect so that it comes up more and I remember it.