Reporting part-time earnings while on benefits after 4 years as a bank teller

I picked up part-time shifts as a bank teller and I am confused about how to report them. I have been trying to stay organised about it. Pay posts on a different day from when I work. Who can I ask without risking my claim?

Thanks for writing this out. I went through something close to it 12 months ago, and it settled down once I kept a simple log of every call and form.