How do I create a additional attribute at rate plan header?

Summary:

In QP_RATE_PLANS table we have additional attributes. But how do we create those DFF/EFF

In Manage Descriptive Flexfields or Manage Extensible Flexfields, I am unable to find any flexfield for rate plans

Content (please ensure you mask any confidential information):

We want to create two char attributes at rate plan headers.
However, with no flexfield task available we are unable to proceed with.

Any help is apprciated

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