I want to use Ctrl +Scroll to zoom in/out in the notebook front-end of Mathematica for Linux 11.3 How to achieve this?
I'm sorry I don't understand.
Which zoom feature are you referring to? 3D graphics zoom? Or Notebook Magnification?
Magnification is found in Menu (this means you can possibly use an OS 'keyboard macro' to get at it), this same Magnification is also an option found in Option Inspector. Option inspector items are (often) functions that can be set by evaluating changes in the kernel. The thing you have to do first (homework, i forget name) is find the Option Inspector item that allows you to filter keystrokes (using that you can build keyboard macros for mathematica - that's what it's for, scanning/altering/substituting keystrokes).
I'm unaware of (in my version - mac version 11.x) of any way to re-assign mathematica's internal "keyboard shortcuts" or if Magnify has a "keybaord shortcut" (in past versions you could, and was displayed under main menu Help quite visibly). but mac has zoom built-in to the magic mouse so i'd be unlikely to use mathematica's.
Because Linux OS there are so many, and each Desktop has completely different macro abilities: commenting on something like "desktop record macro" is impossible
I was, of course, referring to notebook magnification. So you say it might not be possible to add a custom keybinding(Ctrl+"+"/Ctrl+"-") for zooming in/ out?