The subjunctive II is used to express wishful thinking or situations that are contrary to reality. It can also be used to make requests and suggestions sound especially polite.

You're already familiar with the subjunctive II forms of "haben" and "sein" in the present tense, and with the other way of forming the subjunctive II by using "würde" + an infinitive.

Examples:
Wenn das Orakel funktionieren würde, wärst du nicht mehr in der Zeitschleife.
Wenn mir das Orakel helfen würde, hätte ich keine Sorgen mehr.

The subjunctive II can also be used in the past tense. To do that, you use the present perfect - with the helping verbs "haben" or "sein" and the past participle. The helping verbs then take their subjunctive II forms.

Here is an overview of all the forms used in subjunctive II in the past tense.