Enrollment Fast formula to automatically move the Employee's options when the child becomes 26 years

Summary:

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I'm looking for the Fast formula where the Employee's options get automatically moved when their child becomes 26 years and not eligible for the Medical plans.

Eg, if the Employee has 2 children and enrolled in "Employee + Family", it will remain in Employee + Family. If the Employee has only one child, then it gets moved to "Employee + Spouse"

if the Employee has 2 children and enrolled in "Employee + Children", it will remain in Employee + Children. If the Employee has only one child, then it gets moved to "Employee Only"

I know we have a Fast formula to automatically move them but looking for the sample. Please attach the sample Fast formulae in your replies