There seem to be two types of audio configurations for Dell Inspiron 17 R 7720 : 4.1-system and 2.1-system. If you know nothing about under-display speakers this means that your model has 2.1 speaker configuration (front-edge speakers + subwoofer).
Using 5.1 configuration manual by StallionSA when you have a 2.1 will work but it will cause your system unable to produce any sound with some variety after auto-detect procedures (sometimes after reboot or after unplugging headphones). It occures since in 2.1 variant both 0x0d and 0x0f outputs are physically connected to the front speakers, thus interconnected.
For proper work of headphones and subwoofer at Dell Inspiron 17 R 7720 with 2.1 speaker configuration:
You need to have alsa-tools & alsa-tools-gui installed, for example with a console command sudo apt-get install alsa-tools alsa-tools-gui
Select the IDT 92HD91BXX codec
Check the "Show unconnected pins" box
a. To fix no sound issue (totally mute system) restoring defaults once on the go:
remap 0x0d to "Internal speaker" and uncheck its "Override"
remap 0x0f to "Not connected" and uncheck its "Override"
remap 0x10 to "Not connected" and uncheck its "Override"
click "Apply now" button
b. To fix no sound issue (totally mute system) restoring defaults permanently during reboot:
click "Remove boor override" button
reboot your system
c. To make subwoofer work (after your "Pin configuration" settings are back default)
leave 0x0d at "Internal speaker" and check its "Override"
remap 0x10 to "Internal speaker (LFE)" and check its "Override"