The Church has traditionally recited the prayer Adsumus Sancte Spiritus at the beginning of each council and synod.
Whenever bishops gather together to deliberate on important matters in a council or synod, they traditionally recite a special invocation to the Holy Spirit.
According to the official website of the 2021-2023 Synod, this tradition was repeated during the Second Vatican Council.
Here is an English translation of this prayer, which will be used in the upcoming Synod on Synodality.