I have a $14$-$\textrm{bit}$ ADC which can take $-10\textrm{ V}$ to $10\textrm{ V}$ as input. So, $0$ to $16383$ (digital) represents the voltage from $-10$ to $10$. If I want to get the actual voltage from the digital values I am getting, what should I do? i.e. if $8192$ is coming then my program should identify it as $0\textrm{ V}$.

$$V_c=n\frac{V^+-V^-}{2^{14}}+V^-,\quad 0\le n<2^{14}\tag{1}$$
where $n$ is the digital code word, and in your case $V^+=10\,\text{V}$ and $V^-=-10\,\text{V}$.