How do I go about replacing the LCD on my 2014 macbook air?
I essentially need the repair completed within 24 hours


If you need to ask, you do not have the necessary skills, parts and tools to repair it in that time frame.

Also unlikely any service centre can turn it around in 24 hours. 

So your options are:


Get an external monitor. The condition of the internal screen then becomes irrelevant.
Buy a new one, copy your data with Migration Assistant.


Given that the screen is typically the most expensive sub-component, and requires near total disassembly to change, you need to decide between the high repair cost to get an old machine back, or a bit more to get a brand new one with warranty, bigger storage etc. etc.