1. Choose a topic with your assignment's source requirements in mind
Your assignment specifies that you need to develop a video having a historical perspective in the form of a case study and that a modern day case study report is used to make a comparison to modern times.
In that case, there are a lot of topics you WON'T want to choose, because many topics are not written about in case studies. For example, you probably won't find an engineering case study about:
how to tend sheep
Instead, your topic must include:
Decisions and solutions made by civil and environmental engineers
The well-being of the environment or public health
The impact or influence on society, culture, public policy, or the economy
2. Make sure your topic is not too broad
If your topic is a single word or simple phrase, it's probably too broad, like these topics:
the Eiffel Tower
When topics are too broad like this, your writing ends up turning into a long definition. Instead, topics should investigate or analyze something.
Sometimes it's hard to get from a broad topic to a research question that investigates something. To get started, think about your topic in these terms:
Who is involved or affected?
What problem would you like to resolve? Or, what is a possible solution?
When is this topic relevant? Right now, or more historical?
Where (geographically) is the topic relevant?
How did it happen?
Your topic doesn't need to be stated as a question. It could be a statement or hypothesis to find evidence for - or against.
3. Make sure your topic is not too narrow
It's possible to choose a topic that's so narrow, obscure, or weird that NO information sources exist on it - or, at least no case studies. For example:
What percentage of commercial airline crashes was traced to negligent maintenance during the ten years immediately preceding and following deregulation of the airline industry?
That example demonstrates another problem: the answer would simply be a percentage, and you wouldn't be able to stretch that into an essay.
You may need to do a preliminary search on your topic to make sure you can actually find a case study about it. As long as you start the assignment early enough, you should be able to find a topic and a case study no problem!