New Mandatory Memorial: Mater Ecclesiae (Mother of the Church) is to be celebrated on the Monday after Pentecost every year.
On February 11, 2018, the Congregation for Divine Worship and the Discipline of the Sacraments inscribed a new obligatory Memorial of the Blessed Virgin Mary, Mother of the Church, into the Roman Calendar. The mass for the Memorial is already found in the Missal under Votive Masses: 10. Blessed Virgin Mary, B. Our Lady, Mother of the Church. There are new mandatory readings associated with this day that are found here in English and here in Spanish.
You may view everything necessary for praying the Mass and the Liturgy of the Hours for the day on the USCCB website: Memorial of the Blessed Virgin Mary, Mother of the Church.