How to get the value of a capacitor in series if I have the total value
$$ C_T = \frac 1 {\frac 1 {C_1} + \frac 1 {C_2} + ...} $$

Inverting ...

$$ \frac 1 {C_T} = \frac 1 {C_1} + \frac 1 {C_2} + ... $$ 

If \$ C_1 \$ is unknown then 

$$ \frac 1 {C_1} = \frac 1 {C_T} - \frac 1 {C_2} - ... $$ 

Solve that and invert the result to get \$ C_1 \$.