We use the present perfect subjunctive when we want to express a reaction to something that has already happened.
Forming the Present Perfect Subjunctive is easy peasy lemon squeezy.
All you need is the conjugation of the verb haber in the present subjunctive.
Haya Hayamos
Hayas Hayáis
Haya Hayan
Followed by a past participle (you already know what these are!)
For example, I hope that they arrived on time!
Espero que ellos hayan llegado a tiempo.
