Hi @c0mputist
You can replace the keyboard/top cover assembly (it's a complete module), but to do so requires that the entire laptop be disassembled.
Here's the [http://h10032.www1.hp.com/ctg/Manual/c06980363.pdf|maintenance and service guide], taken from this support [https://support.hp.com/us-en/product/setup-user-guides/hp-elitebook-840-g8-notebook-pc/38216725|webpage] for the laptop.
Go to p.74 to view what needs to be done i.e. start on p.43
Also on p74 you will find the HP part numbers for the type of keyboard/top cover assembly and the country that the keyboard is designed to be used in.
Search online for the ''part number appropriate to your particular keyboard type'' to find suppliers that suit you best.
Some examples are:
Keyboard with top cover, backlit, USA = M36312-001
Keyboard with top cover, not backlit, Saudi Arabia = M36310-171