How to auto-fill forms for clients?

I collect initial user data on my Investor Carrot website using their proprietary forms. And, I plan to import user data from these leads to JotForms on my backend Weebly site using an exported .csv file (from Carrot) and Zapier as the translator.

However, the JotForms contain many more data collection fields than my Carrot forms. So, I want to auto-fill my Jotform with exported data from my Carrot form, and send out (links to) a partially filled-in JotForm for my clients to complete.

What's the simplest and most efficient way to do this?

Thanks for your advice,
- Robert

I'm not sure yet if this would help but what we have is the Spreadsheet to Form widget.

How-to-Use-the-Spreadsheet-to-Form-Widget

The widget allows you to import data from an Excel file into the fields on the form once you have entered a correct Unique ID.

May we ask how are you planning on sending the prefilled JotForm to your clients, please? Do you want the link sent to your clients to be prefilled with data from the exported CSV file as soon as they click it? I'm not sure if it is possible, but you need to extract the data from CSV file first then have the data used to create the link which will include URL parameters that will prefill the form — Prepopulating-fields-to-your-JotForm-via-URL-parameters

Thanks Mike -

I'll have to take a look a the widget and get back to you if I still have questions.

In answer to your question, YES. I want Zapier to translate the exported .csv data from their Carrot form into a format that can be used to import (populate) the appropriate data into fields in their JotForm. Then, I plan to send them a link so that when they log into their Weebly account, their form is pre-populated with whatever data they previously provided on Carrot.

I've never done this before, so I'm trying to make the process less confusing and as uncomplicated as possible, for me and for them!

I think combining two ways my colleague suggested may be the easiest way. I recommend you check the guides my colleague share first. I want to share the guides again. 
Guide: How to Use the Spreadsheet to Form Widget
Guide: Prepopulating Fields to Your JotForm via URL Parameters
Firstly you need to prepare your .csv file according to the first guide. After that, you can share the prepopulated webpage URLs to your users. You just need to populate the Unique Code field for each user. For example, you will send a URL like this to a user.
https://www.jotform.us/form/73439222688162?name3[prefix]=rwaldenjr
This form's Unique Code must be the name field.
You will understand what I mean after you read the guides. 
Please contact us whenever you have any questions.