Gerrymandering is complicated. Simplest version; it involves diluting the vote of smaller groups who likely would have been able to vote in representation into the government if not for the interference.
This is done by breaking up that voting group among groups that favor the manipulating party.
The wiki on it does a good job of providing the details.
You are right that anything done can be undone BUT it requires the same level of governmental control. And if you can gerrymander the heck out of the voters, you can pass almost anything.
Note: it is not a purely ‘popular’ vote. That would bypass gerrymandering. Gerrymandering depends on block voting.
“In related news, the director of the Halo TV series will be taking over artistic control.” /s