The correct Active/Passive form of the given sentence is:

☀ I was advised to settle the matter out of court by the Manager.

Explanation for other options:

☀ I had been advised to settle the matter out of court by the Manager. This option uses the past perfect tense ("had been advised"), which suggests an action completed before a certain point in the past. The original sentence does not have a clear context for using the past perfect tense. The correct form should be in the simple past tense, as shown in the correct option.

☀ I have been advised to settle the matter out of court by an Manager. This option uses "an Manager," which is grammatically incorrect. The correct form should be "the Manager" as specified in the original sentence.

☀ I were advising to settle the matter out of court by the Manager. This option changes the subject from "The Manager advised me" to "I were advising," which changes the meaning of the sentence. The original sentence refers to the Manager's advice to me, not my advice to settle the matter. The correct form should be "I was advised to settle the matter out of court by the Manager."