The Catechism in Questions & Answers

659. Are the sacraments also dispensed to the departed?

Yes. In the Sunday divine service and on church holy days, the Chief Apostle and the District Apostles or Apostles commissioned by them also celebrate the sacrament of Holy Communion for the departed after the congregation celebrates Holy Communion. In the process, two ministers serve as proxies to receive the body and blood of Christ on behalf of the departed.
Three times each year—namely on the first Sundays in March, July, and November—special divine services are celebrated in which the Chief Apostle and the District Apostles or Apostles commissioned by them dispense all three sacraments to the departed. These acts are likewise performed on two ministers who serve as proxies.

Help for the departed: see Question 545.

That the sacraments can be dispensed for the dead is clear from 1 Corinthians 15: 29: “Otherwise what will they do who are baptised for the dead, if the dead do not rise at all? Why then are they baptised for the dead?”