Describe the "ideal" state of affairs. There are lots of different ways to write a problem statement — some sources will recommend jumping right to the problem itself, while others recommend providing background context first so that problem (and its solution) are easier to understand for the reader. If you're ever unsure of how to begin, opt for the latter option. While conciseness is something every piece of practical writing should aim for, it's even more important to be well-understood. Start by describing how things should work. Before you even mention your problem, explain in a few sentences how things would be if the problem didn't exist.
For instance, let's say that we work at a major airline and that we've noticed that the way passengers board our planes is an inefficient use of time and resources. In this case, we might begin our problem statement by describing an ideal situation where the boarding system isn't inefficient that the company should shoot for, like this: "The boarding protocols used by ABC Airlines should aim to get each flight's passengers aboard the plane quickly and efficiently so that the plane can take off as soon as possible . The process of boarding should be optimized for time-efficiency but also should be straightforward enough that it can be easily understood by all passengers.