Q. Does a believer have authority to cast out demons, heal the sick, raise the dead?
In other words, we don’t have a blank check simply to “take authority” over any sickness or case of oppression that we might encounter. There needs to be a discernment process in which we seek to discover how God wants us to use the authority he has delegated to us in this particular situation.
Jesus himself said, “The Son can do nothing by himself; he can do only what he sees his Father doing.” And so, for example, when Jesus heard that Lazarus was sick, he first explained to his disciples, ““This sickness is not unto death, but for the glory of God.” In other words, Jesus had discerned that God wanted to use the occasion of Lazarus’ sickness and eventual death as an opportunity to announce the coming of His kingdom. Many people believed in Jesus because of the miraculous sign he did in raising Lazarus from the dead.
However, if Jesus had discerned instead that Lazarus’ sickness was “unto death,” that is, that his “time had come” and God meant instead to bring him home into His presence, then while Jesus would probably still have gone to provide strength and encouragement to Lazarus and his sisters, he wouldn’t necessarily have healed him, or have acted with such authority (“Lazarus, come out!”) if he had died before his arrival.
It’s really hard to imagine this second possibility, however, because Jesus was something of a special case. He actually embodied God’s inbreaking kingdom in his own person. And that’s why we hear over and over again in the gospels that Jesus healed everybody who came to him. It’s hard to picture Jesus not using any occasion as an opportunity to announce God’s kingdom.
But later in the New Testament we discover that Jesus was indeed exceptional in this way. Paul had to tell Timothy in his second letter, for example, “I left Trophimus sick in Miletus.” Even though previously Paul had done extraordinary miracles of healing, in this case he had to go on without a badly needed co-worker because God apparently had a different purpose at work in the situation, as difficult as it might be for us to understand what it could have been.
All that said, I would encourage a person who felt strongly that God wanted to demonstrate His power and presence in a given situation, in order to announce the presence and liberating, life-giving character of his coming kingdom, to pray and act in bold faith, believing that God might indeed use them as a channel to bring about healing and deliverance.
Here are a couple of other posts that relate to this same subject:
https://goodquestionblog.com/2014/06/17/should-we-try-to-heal-people-today-the-way-the-apostles-did/
https://goodquestionblog.com/2014/07/28/why-doesnt-god-intervene-to-relieve-suffering/
Good Question 
I have been asked to go forth and heal by the Holy Spirit and received the Baptism of Fire where I can testify to the existence of the Holy Spirit. I felt dejected and still have doubts about physical healing or raising people from the dead; which, I did once, on a friend who was hospitalised with high diabetes and cholesterol…he is now well and fine and can walk, albeit slowly with a walking stick. I do not know if that’s healing or my strong prayers. I didn’t ask him to get up and walk that’s for sure.
I would say, “prayers” is the ultimatum for any healing.
A believer really must be touched by the Holy Spirit to be a real believer and not by the rituals and reading which is just the beginning of an understanding of religion.