I read this elsewhere on Duolingo lessons; "er" sounds like "air" in a British accent, while "ihr" sounds like "ear" in a British accent, instead.
Reading them that way helped a lot toward me understanding the difference.
It is very difficult to distinguish between Er and Ihr - even in turtle time.
Please avoid these types of questions - having to lose a heart when you do actually know how to conjugate er trinkt and ihr trinkt is frustrating - just because the computer generated voice is misleading.