Here's how it's done:
2. Login to Rebrickable
and hover over "My Rebrickable" and click on "My Parts".
3. Click on "My first part list" and below, there will be an option to import parts from BrickLink orders. Click on the BrickLink orders import and select the XML file:
Once you save your details after uploading your XML list, you can click on "What Can I Build" to start the rebrickable process.