Hi!
I used Virtual Desktop (VR Software you can buy on Steam) and set virtual display distance to about 3.5meters to focus on. I have Pitool opened so I can change values there using arrows on the keyboard in 0.1 steps. Then I focus on something at the center of my view with one eye - the one that is more in the sweetspot with the headset on. I change the offset for that eye until it looks centered. Than I switch alternately between both eyes while trying to keep my view relaxed=focused at far= about 3.5meters while changing the offset for the second eye. the goal is to have the centered object/point ovelapping as precise as you can get it to! remember, for that you might need to adjust the vertical offset for one eye, too.
As eye accomodate fast in VR you might see sharp but your eyes might be crossed! Therefore I lift my headset over and over and focus on something around me at about the same distance as the virtual object and concentrate and try hard not to change that same eyes distance while adjusting offset in VR. It did took me a while to adjust it like that, but there is almost no more eyestrain after taking the headset off. And this is the most important: If you feel some eye strain after taking your headset off and some even slight sensation of looking crosseyed you have to readjust the offsets.
I hope you understand what I mean and hope you can adjust your headset accordingly and enjoy your games. 