Tilt tube turns ?

[steplift20]

I was looking at the steersman nut and want to get it but the problem I'm having ,it's a stupid one, when I try to remove the nut from the port side of the tube the tube turns so I can't get the bolt off, how do I get the bolt off if the tube turns I can't so how do I keep the tube from turning? I know it's easy for you guys but I don't want to screw up now that I have the steering good Thanks for any advice