This is a copy of the instructions for adjusting the M7ii rangefinder in the field. I grabbed it from a Mamiya User Forum thread on the subject. Just wanted to be sure it didn't get lost if their site deleted it. 

As it clearly states: Use at your own risk! You could easily damage your camera if you make a mistake.

By the way, In that same thread someone mentioned that if you are experiencing vertical misalignment, then it may be because you are looking through the viewfinder off-center—try moving your eye around to see if that helps.

Here's the text:

Your comments on being informed on user serviceability are valid, and I would like to address them. As a photojournalist and old Leica user, I understand and appreciate many concerns voiced about being able to adjust the rangefinder under extreme conditions.

I will review the adjustment possibilities of the Mamiya 7 RF with the EXPRESS WARNING that the camera rangefinder assembly CAN BE DAMAGED if adjustment is not properly performed. The following information is shared WITH THE ACKNOWLEDGEMENT AND ACCEPTANCE BY THE CAMERA OWNER THAT THERE IS NO LIABILITY OR WARRANTY IMPLIED BY MAMIYA OP, OR ANY OF THEIR AGENTS, AND THAT IT IS NOT RECOMMENDED TO SERVICE ANY MAMIYA PRODUCT BY ANY OWNER.

If a camera is under warranty, we note that you should send the camera to us, because any user serviceability would void the warranty.

Now that I hope our concerns are clear, on to the information requested in the above forum postings:

The plastic cap at the back of the Mamiya 7 top plate must be removed (you might use an Exacto knife )with care being taken not to cut the body cover ( NOT A GOOD THING ). We use a bit of sealant adhesive to secure the cover.

You might need to replace it with a new plug ( cost from Mamiya America Corp $2.00 USD.) after adjustment is made, because you may cut or damage the plug.

Once removed, there are two screws visible. This is where the delicate part comes in. To service it it properly, we remove the entire top cover and all related parts, which is one reason for the amount of our repair charges on RF adjustment. CAUTION In the field, this is neither desirable nor practical and DEFINITELY NOT for a consumer to perform.

Once the two screws are visible, the bottom one is for infinity adjustment ( screwed into a brass looking part) and the top for horizontal image alignment (chrome on chrome). CAUTION You may see a shielded wire, which you SHOULD NOT TOUCH as it may be easy to cut or damage it. Then you WILL NEED to send the camera in for the top plate to be removed and the wire replaced.

Both screws are very sensitive and are secured with a type of "lock tight" adhesive. DO ONE ADJUSTMENT AT A TIME.

You first need to loosen the adhesive with a solvent like acetone. CAUTION This should be ideally applied SPARINGLY with a needle, and acetone should be used sparingly and not come in contact with anything especially the body cover. It will remove paint.

Once the screw adhesive is loosened ( DO ONE AT A TIME ) VERY CAREFULLY USE THE APPROPRIATE SIZE SCREW DRIVER. CAUTION A wrong size stripped or bent driver head MAY DAMAGE the screw.

CAUTION For infinity, the eccentric screw is very sensitive, and probably needs VERY SLIGHT ADJUSTMENT . You probably need LESS THAN ONE QUARTER turn for adjustment.

Once adjusted, you need to re-seal the screw with A TINY AMOUNT of loctite.

For RF image horizontal alignment, the top screw needs to be loosed in the same manner as above. USE VERY GENTLE adjustment as above, because turning it TOO FAR can DAMAGE THE ENTIRE RF assembly as there are sensitive and some NON-MOVING parts directly connected to the screw. DAMAGING THIS MEANS YOU NEED A NEW RF ASSEMBLY. $$$$. This is why we DO NOT RECOMMEND USER SERVICING.

If you have any further questions, please e-mail us. I hope that this information explains what we do and why we do not recommend user adjustment.

I know many photojournalists who use and abuse the Mamiya 7 in the field daily, and who do not need adjustment as mentioned in the above forum comments. However, in an effort to be responsive, we have shared this information with appropriate caveats.

Hopefully, this explains to anyone who is in desperately in need to adjust their RF in the field what risks they are taking, and what they can do.