For those who have not yet enabled keyboard shortcuts in GMail, perform this precursory step: Use this google help article to enable keyboard shortcuts in GMail. Further down in the article, you'll see steps to customize keyboard shortcuts. If the link is dead, the current steps are GMail's Settings > General tab, Keyboard Shortcuts: on. Then, possibly after page reload, within GMail settings, you should see a new tab, GMail's Settings > Keyboard Shortcuts.
Navigate to Keyboard Shortcuts in GMail's Settings and scroll to the Delete Action.
Next, we have to copy the character used to represent the press of a delete key. We have to do this part manually because Stack Exchange removes the character when posting, so it cannot be provided within this answer. The ASCII no. for delete, is 127. Input that number into ASCII number to char convertor, click 'Convert to String', then 'Copy to Clipboard' to obtain the symbol.
Paste that symbol next to the Delete Action in GMail's Keyboard Shortcut's tab. Click Save Changes at the bottom.
DEL
key.DEL
key. This is why my question was only related to theDEL
key of the keyboard. I tried to type DEL in the Custom keyboard shortcut section but it doesn't work.