IELTS Writing Task 1: 'overview' not conclusion
You don't need to write a conclusion for IELTS writing task 1. You need to write an "overview" of the information.
But why don't you need to write a conclusion? What's the difference between a conclusion and an overview?
First, a conclusion is really a final judgment, decision or opinion. This is perfect for the task 2 essay, but task 1 asks you to write a description without analysis or opinions. On the other hand, an "overview" is a simple description of the main points. It is a summary of the information shown in the graph or chart.
Second, a conclusion should be at the end of a piece of writing. An overview or general summary could go either at the end or near the beginning. Personally, I think it's a good idea to describe the main features of the graph or chart near the beginning of your essay.