Can the fileds be auto filled from existing data based on a submission done last month?

I'm afraid that's not doable. You can prepopulate a form using URL parameters but that only gets triggered on form submission. Existing data from previous submissions would need to be manually keyed in.

If what you need is sort of edit existing submissions, you can do that anytime by following the guide I'm linking below.

Complete guide: How-to-Edit-Submissions-Made-on-Your-Forms 

Since I'm not sure what your end goal is with this kind of setup, giving us more info will allow us to better assist you. So, if you need more help, just get back to us with a bit more info and a clearer description of what you're trying to do.