§ 1. A plenary indulgence is granted to the Christian faithful who, in a church or in an oratory, are present [take part] in a recitation or solemn chant of: …
1° the hymn Veni Creator … on the first day of the year, imploring divine assistance for the whole of the coming year…

2° the Te Deum hymn, on the last day of the year, in thanksgiving to God for the favors received in the course of the entire year.

(Reference: Enchiridion Indulgentiarum, 4th editional. concessiones.)
The indulgence is acquired under the usual conditions. i.e., to Confess mortal and venial sin within eight days prior to or after the day on which the indulgence is offered, to pray for the intentions of the Holy Father.