You will find plenty of resources that will explain when to use the subjunctive mode in French (eg https://www.thoughtco.com/french-subjunctive-rules-and-examples-1369323) , but I think you should not think of the subjunctive present forms as having “imperfect endings”, this is maybe why this is confusing for you.
In the 1st and 2nd person plural of the subjunctive present, it is true that the endings will be “-ions” and “-iez”. These indeed HAPPEN to be the same endings as you would have for the indicative imperfect – but that does not mean that these endings would be used only for the imperfect or even for expressing a past action.