Comment 2 for bug 1812758

Have you used the service tag to see if you can get a link to the Dell Ubuntu 16.04 installation images?

"For those who purchased their system from Dell with Ubuntu already installed, there are recovery images on their system and if fitting a new hard drive they can download an installation image by going to the Dell Support site and entering the systems service tag or express service code and selecting Drivers and Downloads."

From https://www.dell.com/support/article/uk/en/ukbsdt1/sln151664/how-to-install-ubuntu-linux-on-your-dell-pc?lang=en

Alternatively you may need to contact Dell support directly - that might be the better option here since presumably Dell have configured these images to 'just work' and save you some time needing to debug it.