How to downgrade an iPhone 7 Plus to iOS 10.x.x without SHSH???

Hello, I am a high level computer expert, I know about device factory manufacturing precisions, workaround and more, and I need to be enlightened in the procedure I would like to consider: downgrade iPhone 7 Plus to iOS 10.x.x, and without SHSH, whatever the workaround method for this procedure, I am ready to be told about +++ skills, use of very advanced software and specific workarounds, no worries I would understand absolutely everything.

Thank you for being able to enlighten me as best you can. 😊