Hi Verena,
Have a look at the website Engage for Success. It should have some useful tips for you plus reference papers: https://engageforsuccess.org/

What provider are you with? I assume that you have had to discuss the topic structure with your tutor, so you will have an outline of the question you are answering with regard to retention.
I looked at recruitment and retention, too.
The key is to read around the topic. Go into EBSCO via the CIPD website and download lots of papers. You might be surprised what you'll find. Once you've read your first 10 or so papers you'll get a much clearer idea of the particular areas that interest you and can target search for more papers.
This was the module I read the largest numbers of papers for (and didn't even use half of them in the assignment that followed). So reading is a good starting point.