How can employees re-rate themselves on a validated skill?

Summary:

In Skills Center, how can employee re-rate themselves on a skill that's already been validated? For example, an employee rates themselves as a 2 (on a scale of 1-5) on a skill called Negotiation Skills and their manager endorses that skill rating. An employee then works to increase their proficiency on that skill and wants to re-rate themselves as 3 and re-request the endorsement. How is that action taken? In Skills Center, it looks like as soon as the skill is validated you can no longer change the proficiency rating.

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