You must have often heard this advice that the introduction of your thesis should be the last thing that your write. If you go by this advice, it is evident that you would be writing your introduction and conclusion not much apart from each other. It can get confusing to understand what to be put in which chapter. Do not get intimidated by this because all you need is to be clear what the component of each of the chapters is.
Firstly, you must know the difference between introduction and conclusion. Introduction is your state of knowledge that is prior to your research and conclusion is your state of knowledge after you have completed your research. So your introduction should bring up the questions you have attempted to answer in your research and your conclusion should raise new questions that have erupted from your research. In your introduction, try to outline the problem you are trying to solve and also place those problems in alignment with some broader situation. It could also be a problem of the real world towards whose solution your research could be one step forward. When you write your introduction, it should be elaborated in such a way that it leads your research topic and expands it in a way that the reader feels equipped enough to understand the application part of the research in the subsequent chapters. There are many ways to write an introduction, but the general and most acceptable rule says only as far as describing the problem. For the remaining content there are the subsequent chapters.
If you have got confused about what to put in the conclusion chapter now and worried that it doesn’t replicate the introduction then you must know very clearly that here you need to write the new thing that you know now, which you weren’t aware of before the research happened. Link it up with the earlier similar published work, and mention whether your research supports it or opposes it.
Essentially, it should also include those further questions that arise after your research and create the path for any further potential research that could be carried out. The best and easiest advice is to keep the introduction and conclusion simple so that the reader does not miss the main message you want to give from this research and remember as the gist of your thesis.