Hi,
The command ChangeCovD[expr, covd1, covd2] changes the covd1 derivatives into the covd2 derivatives, introducing appropriate Christoffel tensors. Both covd1 and covd2 can be PD. For example, suppose this setup:
<<xAct`xTensor`
$PrePrint = ScreenDollarIndices;
DefManifold[M, 4, {a, b, c, d, e}]
DefTensor[v[a], M]
DefMetric[-1, g[-a, -b], cd]
Then take an expression like this:
PD[-a][v[b]] + v[-a] v[b]
You can change PD to CD using
ChangeCovD[%, PD, cd]
Cheers,
Jose.