In the book Gravitation (Misner, Throne and Wheeler), it's said that to consider the line element of the flat space on the derivation of Maxwell tensor $\bf{^*F}$ from the Fadaray tensor $\bf{F}$ (text before equation 4.15).
How do I construct the Maxwell tensor $\bf{^*F}$ from Fadaray one $\bf{F}$ in a non-flat spacetime, once the unique equation presented in Gravitation is using the "Levi-Civita tensor" $\epsilon_{\mu\nu\alpha\beta}$ by
$^*F_{\alpha\beta}=\frac{1}{2}F^{\mu\nu}\epsilon_{\mu\nu\alpha\beta}$
and not the metric tensor $g_{\mu\nu}$?