Login to your account and Press your Icon in the upper right corner and select Data Migration > Add New Files.

On the next screen, you will select a Provider, or what source the data is from.

Next you will choose what type of files you want to upload. You can upload one file for each: Customers, Estimates, Invoices, Work orders, Items and Categories, Expenses and Others. 
Press Upload for each file type you want to submit

If you have any messages or notes about the file types Markate should know about, you can use the Message box.

When you are finished, press Submit. 

Markate will update within 1-3 business days! 

Here is the video showing you how to do this.