Validation rule will applicable to existing record also but it will fire when you update those records, because validation rule fires on every DML operation. So to make it applicable for existing records you need to update those records.
If this solves your problem, kindly mark it as the best answer.
Validation rule will applicable to existing record also but it will fire when you update those records, because validation rule fires on every DML operation.
So to make it applicable for existing records you need to update those records.
If this solves your problem, kindly mark it as the best answer.
Thanks,
Vatsal