I think what you are asking is: you get the scope crosshairs level, then when you tighten the rings it turns the scope.
Yes, I have pulled my hair out from that myself. I really don't have a solution other than trial and error. I have tried everything I can think of from putting the scope on so that by tightening up the rings, it will bring it to level. I have tried being very aware of tightening the screws with the same amount of torque, I have tried continuously checking and if it starts to turn I tighten the screws on the other side hoping to bring it back to level.......... In the end, I tried everything over and over until the crosshairs were level and thanked the almighty that it was over. Some rings seem to do this and others don't. I have mounted probably a hundred scopes and on the rings that do that, it is nothing but frustration.
If you are asking how to get the crosshairs level: I have a set of levels from Wheeler Engineering: you can get them at Amazon, Midway, Brownells............ You sit one on the action and one on the elevation turret of the scope (they are magnetic) and make them agree that the scope is level. I have also used a plumb bob. I also have some kind of scope leveling device that has a square rod that goes though the rail on the rifle and it is intended to be used to align the crosshairs with it by eye. I basically only use the thing as another level: it has a bubble level on it and if I can't put one of those Wheeler Engineering levels on the action for some reason (like the magnets don't stick because the action is aluminum or there is no room for the level).
On my long range rifles, I also have a level on the rifle or actually they are mounted to the scope tube so that when I am firing the rifle, I know it is level. Obviously after getting the scope mounted and level, I then make the last level agree with the other two levels.
Yes, it is much easier to do this if you have the gun in some kind of cradle. I have a gun cleaning cradle thing that I bought from Midway 20 years ago or so.