pkg install -f <packagename>
. But keep in mind that this won't overwrite existing configuration files.In that caseI think the OP may be asking about the configuration of the port for building not the one for running of the port...
make rmconfig
or make rmconfig-recursive
will remove any configuration you've done (and thus go back to the defaults). rmconfig Remove OPTIONS config for this port.
rmconfig-recursive Remove OPTIONS config for this port and all its
dependencies.