In my experience, I prefer to run reports out of my existing system (in this case HubSpot) and get them into Excel. I've never used HubSpot but I would be surprised if you can't get the data you want into Excel. So, use RPA to run the report and open Excel.
Now that you have all the data in Excel, you have all the information you need. If the legacy CRM has import capabilities (say from csv), then manipulate the data in Excel and import it into the legacy CRM. If not, just have RPA use the UIs and enter the information one row at a time, looping on the Excel Data.
If you need an input from the user at certain points there is a Message Box, where you can tell them what to do, or there is an InputBox where you can ask for a specific value or entry. I use a message box when I need human interaction. It may be a link I can get to via UI or something, so the message box appears and says "click All, then click OK here" so the flow pauses until they click OK. For the InputBox, I had prices that had to be gotten from 7 different sites, so the flow went to the website and put in the dates and everything, but rather than spend hours trying to get the price from the html code of each website, I decided to just have the user look for it real quick and input it in.
Best of luck!
