DETROIT—One of six men charged in an alleged plot to snatch Michigan Gov. Gretchen Whitmer has agreed to plead guilty to a kidnapping conspiracy, according to a court document filed Wednesday. The filing was made by prosecutors ahead of Ty Garbin’s appearance in federal court in Grand Rapids. The plea agreement signed by Garbin indicates that he will “fully cooperate” with investigators. There is no agreement on his sentencing guidelines. The FBI in October said it broke up a plot to kidnap the Democratic governor by anti-government extremists upset over her coronavirus restrictions. Six people were charged in federal court while eight others were charged in state court with aiding the alleged scheme. In the plea agreement, Garbin admitted to more than five pages of stunning allegations. He said he and others trained with weapons in Munith, Michigan, and Cambria, Wisconsin, last summer and “discussed the plan to storm the …