How can I see whether I have checked in a movie before?

On the browser version of IMDb, you can look on the title's page whether it's checked in using the drop-down for adding the title to lists. It's the down arrow to the right of the "Add to Watchlist" button. You may need to scroll through your lists to find Check-ins.

@bderoes Thanks for your response. I knew this about the browser version, and that's where I go when I need this. But I'm trying to find a similar function in the Android app -- that's why I posted the question in the Android app section here. FWIW, there is an "Add to List" menu item in the Android app that works similar to what you describe -- but weirdly it doesn't show the "Check-ins" list.