The missing part of the equation is simply the identity factor, which means no additional conversion is needed. Therefore, the equation is complete as given:
\[
\boxed{\left(-3.4 \times 10^{4} \frac{\mu \mathrm{~g}}{\mathrm{dL}}\right) \cdot\left(\frac{10^{-12} \mathrm{~g}}{1 \mu}\right) \times\left(\frac{1 \mathrm{dL}}{100 \mathrm{~mL}}\right) = \frac{\mathrm{~g}}{\mathrm{~mL}}}
\]