Did mistake of doing PhD in a dead field. How to approach postdoc applications with hope of changing fields?
To some extent, it's expected that you're not an expert in the field of the post-doc. One of the points of doing a post-doc in the first place is to broaden your research profile.

The thing you should be worried about is your track record - from the prospective advisor's side, one of the most important questions is whether you're able to effectively finish up a research project. If one finished publication is way beyond in the norm in your field, then you should indeed be worried; if it is the norm you may be fine.

The other aspect is to put up a convincing job letter that will explain why you are the right fit -- you may want to emphasize relevant skills and experiences and explain how they will help in the job you apply for.