Therefore, when a Catholic priest prays a blessing of mercy on a couple in an irregular situation, who “desire to entrust themselves to the Lord and his mercy, to invoke his help, and to be guided to a greater understanding of his plan of love and of truth” (no. 30), he is asking God to have pity on both of them and to give them the grace of conversion so that they can regularize their relationships.
This blessing of mercy is not and cannot be a blessing of sanctification since we cannot ask God to bless something that, as Fiducia supplicans explains, is not “conformed to God’s will, as expressed in the teachings of the Church” (no. 9). Priests who are invited to bless couples in irregular situations should choose the appropriate words to reveal this intent of the Church.
https://cbcpnews.net/cbcpnews/full-text-archbishop-villegas-issues-guidance-on-vatican-declaration-fiducia-supplicans/