This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
勆 combines 良 and 力, but the exact historical development is uncertain. It may have originally expressed strength or goodness related to power, but this is speculative.
The left side 良 suggests good, and the right side 力 suggests power. Imagine a person with good strength, but the exact meaning is unclear.
For ロウ, imagine a strong person rowing a boat: row -> ロウ, and the power 力 comes from good 良 effort.