For Mint you could maybe repurpose the Debian instructions (install the firmware-iwlwifi package): wiki.debian.org/…/Latitude7490
But I guess it’s a weird issue since Intel cards are usually well supported. So are most Dell laptops in general. My usual approach is to type in something like “wiki linux dell 7480” into google. There are very little specific info around which leads me to believe everything usually works out of the box.
In case the thing with the button holding and power cord doesn’t work, check your BIOS settings if it’s disabled somewhere and then check the logfiles. “dmesg” and the boot output might contain the exact issue.