When installing Mycelium, the first time it asks whether to start a new wallet or restore a previous backup.

However, once a new wallet is running, is it still possible to import a HD backup (12 words) from another wallet? Or better yet, (temporarily) switch to a different HD wallet, by entering 12 words?

The problem is: I recently installed Mycelium on my phone, started a new HD wallet, but now I suddenly doubt if my old wallet still had some bitcoins left. I still have the 12 words (for both the old wallet, and the new one). But I can't seem to open or restore or import an old wallet anymore, once a new HD wallet has been created??