How do I set the Device Placement setting?

I cannot reproduce the screenshot you presented. “Details” are at the top of your screen - I cannot reproduce that. I don’t know where “Back” goes in the upper left.

Assuming your iPhone is the only device supplying data for walking steadiness, device placement is irrelevant. I have waking steadiness statistics from my iPhone without any placement consideration.

“Device Placement setting”?

• What device?
• What placement?
• Is an Apple Watch involved?
• What type(s) of measurements?