To import a Custom HTML Block 

1)Unzip the template zip in your local
2)Go into your Header or any other page in the builder and Press "Edit"
3)Click on the "Block Manager"
4)Press Import and upload the blocks-comp-1.zip (name might vary) *Do not unzip the HTML Blocks .zip should be uploaded as a zip.

To Import Custom .CSS or .JS

1)Unzip the template zip in your local
2)Go into your Header or any other page in the builder and Press "Edit"
3)Click on the "Import CSS and  JS"
4)Use the import button to upload your custom .css or .js