Jesus and his apostles healed many people! Mark 6:13, “…And they were casting out many demons and were anointing with oil many sick people and healing them.”
But, they did not heal themselves. The Apostle Paul prayed to be relieved from what appears to have been a physical ailment, but was told that God’s grace would help him get through it. 2 Corinthians 12:8, 9: “Concerning this, I (Paul) implored the Lord three times that it might leave me. And He has said to me, ‘My grace is sufficient for you, for power is perfected in weakness.’” Paul accepted that.
It is not improper to pray for relief from physical suffering. However, it is important to recognize that our sufferings, both physical and emotional, develop our faith and our characters. James 5:10, 11, “Take, my brethren, the prophets…for an example of suffering affliction, and of patience. Behold, we count them happy which endure…” Thus, our trials, temptations, and even physical suffering teach us to rely on Christ’s power. The Apostle Paul emphasized this when he wrote, “…Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.” 2 Corinthians 12:9.
Can Christians heal unbelievers today? No.
The miracles, which Jesus and the apostles did, were to show us what the future kingdom of God on earth will be like; all people’s physical, mental and spiritual sicknesses will eventually be healed. (See Isaiah 35.) But, these wonderful miracles stopped when the apostles died. The purpose of the gifts of the spirit (including tongues/foreign languages and healing) was to verify to unbelievers that the gospel message was true. These miracles helped to establish the early church. Now, however, because God has given us the full New Testament, the gifts have ceased. Now, we no longer need miracles to establish our faith as we have the “more sure word of prophecy.” (2 Peter 1:19) The Bible is completely sufficient for our conversion and development. “All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work.” 2 Timothy 3:16, 17.