The Catechism of the Catholic Church teaches:
“All who die in God’s grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven.” (CCC 1030)
The next web page are prayers you can pray for those in Purgatory who always will need our prayers. And by also making sacrifices for these Holy Souls, we help shorten their time in purgatory especially those on the brink of entering eternal rest. Our prayers hurry their time to unite with our Merciful Savior.
Pray: Eternal rest grant unto them O Lord and let perpetual light shine upon them. May the souls of all the faithful departed, through the Mercy of God, rest in peace. Amen.
The Holy Rosary is a powerful prayer of interceding for poor souls. The Rosary helps to bring release & relief for the suffering souls, but the indulgences that come with praying our Lady’s rosary brings great merit for all of us.
Praying the Chaplet of The Divine Mercy, which Our Lord encouraged St. Faustina to say, is a huge help to these souls. Our Lord encouraged her by saying: "My daughter, encourage souls to say the Chaplet which I have given you. It pleases Me to grant everything they ask of Me by saying the Chaplet. When hardened sinners say it, I will fill their souls with peace and the hour of their death will be a happy one" (Diary, 1541).
Bring forgiveness into your prayer for those you specifically pray for…here is a full writeup on The Divine Mercy website: How to Intercede for Poor Souls | The Divine Mercy
Here is a link with several topics on Holy Souls in Purgatory Holy Souls Sodality | The Divine Mercy Look to the length of video to fit you time of day.
A page 2 link to a Feb. 15, 2019, article: 'We Must Pray for the Deceased' | The Divine Mercy plus others.
A December 16, 2018, article: Purgatory and Psalm 130 | The Divine Mercy