How should I use this OTP region

Hello,

It is possible to store data in the OTP registers during production programming if that's what you want. As an example, here is how you can use nrfjprog with a J-link programmer to set UICR.OTP[0] to the value 0x123456

$ nrfjprog --memwr 0xff8100 --val 0x123456 // Store value

$ nrfjprog --memrd 0xff8100 // read back value from the same UICR register to verify the content

Here is some additional reading relevant to the OTP registers that you may want to take a look at as well: Protecting the UICR content, Writing to user information configuration registers (UICR), NVMC protection mechanisms.