The phrase "to annul the election" means canceling or invalidating the results of an election, declaring it void and having to redo the process. Full definition
Unfortunately, the earlier concurrent decisions of the Governorship Election Petition Tribunal and that of the Appeal Court annulling the election of the Rivers State Governor, Nyesom Wike, were upturned by the Supreme Court of Nigeria yesterday. (nigeriapoliticsonline.com)
Speaking on national TV over the weekend, President Jammeh announced his «total rejection of the election result... thereby annulling the election». (ghanapoliticsonline.com)
But he came out on December 9 to annul the election results and demand a re-run, thereby going back on his earlier concession. (citifmonline.com)