The company—and your boss—owe you a big one after promoting you to acting manager and then demoting you when the old manager returned
When my boss left the company about six months ago, I was promoted to acting manager. I can see now that I should have asked my manager (who had been my boss's boss until she left) why he made me acting manager instead of just manager, but I assumed it was because I had never been in management before.
I think I did a good job in my new role, and my manager seemed pleased with my performance. But now my old manager has returned because the company she joined went out of business and she is back in her old job. I've been bumped back down to the rank and file, and I'm not sure what to do. Any suggestions?
I am sorry to hear about your situation, but I also see a learning opportunity in it. (Learning is so much easier in hindsight, isn't it?) You are right: You should have asked your new manager at the time you were promoted, "What will it take for me to become the full department manager?" The two of you would have mapped out a set of performance goals and a timeline.
Now that your old manager is back, when things settle down you and she should have a long conversation. Let her know that as glad as you are to see her again (cross your fingers behind your back while you say it if this isn't the 100% truth), you are also disappointed that your first foray into management was short-circuited. Talk with her about your desire to get back into a leadership role and enlist her help in getting you there. She owes you one!
You can be your usual pleasant self, but also be steadfast as you discuss your aspirations. It isn't appropriate that the company bumped you back into the chorus line without so much as a thank-you when your manager returned to the show. The company owes you one, too. You can say, "I really enjoyed my assignment as acting manager, and it is important for me to get back into a leadership spot as soon as I can."
With luck, your new/old manager will become an advocate for you and will take her role as your leadership trainer seriously too. If you give it some time (say, a year) and don't see any promising signs that this company sees you as a manager (except when they're behind the eight-ball) you should begin to look at other employers and their leadership opportunities as well. You stepped up when the company asked you to, and it's only right that they should support you now in moving toward the leadership position you seek.