Roll the engine over by hand and watch the valve action so you can see how much "turning" is required to open then close the valve and get a feel for it.
When you know the lifter is on the base circle (hopefully in the middle of it when there is NO lift), you can adjust the lash on that valve. Repeat this until they are all done.
There are more scientific ways, but this works just fine. And if you leave the plugs in, it's good exercise.
Ronnie