In most (in all, afaik, but there are a lot, so I don’t want to paint with too broad a brush) dialects of Spanish, /n/ and /ŋ/ are allophones, with /ŋ/ occurring preceding another velar sound, like the n in cinco, conga or conquistador (I’m sorry for the examples, they’re just the first ones that come to mind).

Maybe try contrasting cinco:cinto and conga:conta at first (or other minimal pairs with an n preceding a velar consonant vs an n preceding any other phone). It should be easier to distinguish in your native language first, then to apply it to languages you’re learning.

Even if you’re 50:50 on minimal pairs in Spanish, if you practice it for a few minutes most days, you should see some improvement.

If you don’t after several weeks, there might be an auditory issue or something similar (or you might just need a different approach, though this is generally the fastest way to sensitize yourself afaik), but that still won’t prevent you from being able to become fluent if that’s your goal- you just might have an accent and need to clarify some things. But given that Beijingers are beginning to blend the sounds, you might also encounter few issues related to this that get in the way of fluency.

Your account is almost 3 years old, though? Edit: Oh, it's probably complicated, never mind. As you were.