You have a couple of options available where you can pass the details from the first survey into the follow-up survey.
You can merge the sample from the first survey into the the follow-up survey or you can use the survey links in the follow-up survey to pass the data in.
Click on the Access button, define a password under the Passwords Fields tab and your merged fields under the Merged Fields and be sure to define their data types. You can also mask your password field and make it case sensitive. Create a CSV file of the sample and be sure to name the sample fields exactly the same way you named them within Sawtooth. Click on the Password data button at the bottom, then when the new window opens, click on the Import button (again at the bottom). Browse for your CSV file and import. Click the tick button to ensure their are no duplicate passwords present.
Click on the Access button, define a password under the Passwords Fields tab and your pass-in fields under the Pass-In Fields and be sure to define their data types. Add your data fields to the end of your survey link (see example below).
[You survey link]&Name=Fred&Age=47&City=Dallas
So any of these 2 options will have you passing data into your follow-up survey.
I prefer option 1 as the data is not visible within the survey link.