What Bev said. If you're using ISO as "motivator" you're doomed from the start. You need to make changes because they make good business sense, not because ISO says so.
Agreed. ISO serves the business. not the other way around.
Back to OP: Step one: ban the word ISO on the floor. Literally. Do not say it. Do not say compliance, Do not say auditor, Do not say requirement. When production people hear those words, they immediately feel powerless and unable to leverage their expertise in the process.
Instead you talk about rework, scrap, getting yelled at for things upstream (lack of control on their work quality)
Step two: give them control levers, not an SOP. You do not walk in with a finished process. You walk in with a question. "Hey Joe, where does this job usually go sideways?" Then "If you could change one thing here that would make your day easier, what would it be?" Then shut up. Don't interrupt or offer solutions as they speak. They are providing witness testimony to you, which you can't always find in data and spreadsheets.
It signals respect. It shifts ownership. Make the new rule(s) protect them immediately
The first time Joe uses the control and QA backs him, you lock it in. Now Joe sees you as a part of his team.... and if something goes wrong while he follows the rules, you MUST defend Joe & production always.
