You can plot the line using xline() and then merely update it's Value property to move it. The line's handle must be stored as an app property.
2) Plot the line somewhere in your code (a callback function or at startup) and store the handle.
app.verticalLineHandle = xline(app.UIAxes3, 0); % this plots the vert line at x=0
3) In your button callback function, all you need to do is change the value of the line to move it.
app.verticalLineHandle.Value = 1; % Now the line is at x=1
