"To rig the election" means to manipulate or cheat the voting process in order to ensure a desired outcome or to gain an unfair advantage in an election. Full definition
What I said was that I had a vision that there was an attempt to rig the election in favour of one of the candidates, and this could lead to violence and confusion. (ghanapoliticsonline.com)
How can the APC rig an election which only the APC contested? (punchng.com)
With dedication and being very vigilant at, especially, the polling station level it may be difficult for one party rig the election. (citifmonline.com)