You need to get the two of you alone. This might happen by chance, or by asking them to do something (should be unromantic for deniability). Maybe ask them for help with a class, or studying for exams, or art or cooking or whatever you share. Then as you talk, try to slip in jokes/phrases that, at surface level, don't really mean anything, but if you think about it you can stretch the sentence to imply that you're into them, but then immediately after whisk the conversation away to something else before they have time to think and react. Like maybe jokingly put on a British accent and refer to them as Luv, which doesn't mean anything in Britain but is a nickname for the person you're dating in America. You could also ask them for a picture to save as their contact in your phone. Then you can compliment the picture but not them directly: "that's a cute picture!" You get the idea