I hope you were not "directed to" use ProConnect Tax but have chosen to do so of your own volition after test driving the software, especially if you are used to form-based input, customization, and/or reporting, none of which is not available in ProConnect Tax. ProConnect Tax does have its strengths but it really depends a lot on the profile of your clients and whether you prefer cloud-based tax products.
Going back to your question: The data conversion process is relatively straightforward. You can refer to the following articles for instructions and an overview of what converts from the different tax programs, including ProSeries -
Still an AllStar
I am in the same position as the OP - I used ProSeries for 30 years, and I'm in the process of retiring and doing about a dozen paid returns for certain special clients, which makes the cost of ProSeries prohibitive (even PPR requires a minimum that is too high). So Intuit recommended ProConnect. It is what it is - it's not great, but I can make it work for these very simple returns.
That being said - the data conversion process is really bad.
I followed the step by step instructions and successfully converted ten returns from 2019 ProSeries to 2020 PCTO. It's annoying that the screen for copying the installation key has a "Next" button which does NOTHING except cycle you through the setup again - and there's nothing on that screen that says: "Now run the Data Conversion Tool directly from your start menu or desktop".
So today I wanted to add another 2019 client to PCTO, and I again followed the step by step instructions - but I hit a dead end in the Tool, right after the screen where I tell the conversion program which software and year to convert from - because the next screen was "The following files will be sent to Intuit to be converted" - and it was just a list of the ten clients I already converted. That's it - submit those same clients for conversion again, or go back to the "What program and year" screen - these were the only choices.
Here is what I finally figured out - and I did this by going back and telling the conversion tool that I was converting from Lacerte instead of ProSeries. By doing that, the program allowed me to continue to the "read these instructions for backing up data files" which is the part I had forgotten about after doing the first set of conversions. It's bizarre that these instructions are so hard to get to. They don't exist in the online Help. Anyway, I only had to extrapolate a little bit on the specifics, as they were LC instructions instead of PS. Once I realized/remembered this essential step and got my new selections backed up to the ConversionData directory, the tool added the new files to the list of converted or convertible files and I could proceed.
My review: the data conversion process is awkwardly designed and really badly executed, and the online instructions are obscure and definitely incomplete with any reference to the backup instructions.