The 5th Council’s anathema against Origen:
IF anyone asserts the fabulous pre-existence of souls, and shall assert the monstrous restoration which follows from it: let him be anathema.
The “restoration” refers to apokatastasis, which for Origen is the eventual “restoration” of all intelligent creatures to God. It is called a “restoration” because for Origen, human persons pre-existed in the realm of closeness to God, and humans will eventually (even after eons in hells) enter into God’s realm.
Thus, this anathema only addresses the belief that (1) there was an original status of closeness to God, a pre-existence before birth; and that (2) eventually, even after eons, all intelligent beings will be restored to their original state. This was Origen’s view of universalism.
St. Isaac the Syrian, St. Gregory of Nyssa, and any other Christian universalists were not condemned by this council, nor by any council, because they did not argue for a pre-existent state of closeness to God. They simply argued for the eventually salvation of all intelligent beings. That simple statement, as of yet, has yet to be condemned by council.
Heck, even this condemnation against Origen was not approved by the council.
But back to the OP:
On the issue of praying someone out of Hell: the Orthodox believe in the Last Judgement as the time when eternal damnation and eternal salvation begins in time. We can give “eternal damnation” the specific term “eternal hell”. Thus, eternal hell doesn’t exist yet, because the Last Judgement has not happened.
Thus, for the Orthodox, eternal hell does not (yet) exist, so you can’t pray anyone out of it.
What does exist is the state between death and Last Judgement. We can call that state “hades”. Hades is, by its very nature, temporary. For the Orthodox, Hades is not a place of punishment, nor flames, nor even a teeny, weeny bit. However, in Hades, one may have a vision of one’s future Last Judgement status, and if your envisioned status doesn’t seem too rosy, you might want to have the Church on earth offer up a few prayers for you. Even if you think you are on the way to eternal hell, while waiting in Hades, you are not in eternal hell just yet, and there is always hope that the Church will pray you out of your current probably trajectory. For the Orthodox, there is always hope for salvation, until that last curtain call.
It’s not over, until the skinny lady sings.