They appear in 1 Timothy 1:20.
Thanks for your question.
Hymenaeus and Alexander as well as Philetus were converts in Ephesus mentioned for their false teaching in 1 Timothy 1:20 as you noted but also in 2 Timothy 2:17.
Already at that time, the false notion of the immortality of the soul was beginning to creep into Christianity from Greek philosophy. They taught that the resurrection was past. That is that the Resurrection of Jesus was the one and only resurrection and that the resurrection promised to believers was only a parable designed to teach the freedom of the soul to immortality of one who comes to Christ. Paul teaches against the doctrine powerfully in many places but nowhere more forcefully than in 1 Corinthians 15.
1 Corinthians 15:12-19 Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead? 13 But if there be no resurrection of the dead, then is Christ not risen: 14 And if Christ be not risen, then is our preaching vain, and your faith is also vain. 15 Yea, and we are found false witnesses of God; because we have testified of God that he raised up Christ: whom he raised not up, if so be that the dead rise not.
16 For if the dead rise not, then is not Christ raised: 17 And if Christ be not raised, your faith is vain; ye are yet in your sins. 18 Then they also which are fallen asleep in Christ are perished. 19 If in this life only we have hope in Christ, we are of all men most miserable.
Notice how he emphasizes the importance of resurrection. He says that without it, there is NO HOPE! If we have an immortal soul that argument makes no sense. Most churches today actually teach the doctrine of Hymenaeus and Alexander which Paul so clealry condemns.
Here is some reading material from the website which will assist you in understanding true Bible teaching about life after death.
I hope you have found this helpful.