This will be the least useful photo in the history of this site, but anyway…
Clamp the head into a vise. Use wood blocks to protect the head.
Wrap masking tape a few times around the neck.
If you want to adjust loft, slip the first crescent wrench on from the heel side. If you want to adjust lie, slip it on from the face side. Tighten it.
Slip the second wrench onto the head or handle of the first wrench. The second wrench will be in the same orientation as the bend direction. Use it to make the first wrench bend the neck.
I already did the loft on this one, then stuck it back in for the photo. If I was doing lie, the putter would likely slip in the vise. In the past I’ve had to clamp it toe down in a vise for lie adjustment.