By doing what Jesus said to do and repenting of his sins.
No.
Paul wasn’t saved yet on that road to Damascus when he finally believed.
Acts 9:6 And he trembling and astonished said, Lord, what wilt thou have me to do? And the Lord said unto him, Arise, and go into the city, and it shall be told thee what thou must do.
Paul was not saved as soon as he believed Jesus on that road to Damascus. This proves faith alone is not a true doctrine. Paul had to find out what he had to do; Jesus told him where to go, Paul obeyed and went. Paul did not eat or drink for three days, and he spent that time praying.
Acts 9:9 And he was three days without sight, and neither ate nor drank.
Can you imagine the prayers of Paul?! Paul no doubt was crying and asking God to forgive him for all his sins.
Acts 9:11 The Lord told him, "Go to the house of Judas on Straight Street and ask for a man from Tarsus named Saul, for he is praying.
Acts 9:17 And Ananias went his way, and entered into the house; and putting his hands on him said, Brother Saul, the Lord, even Jesus, that appeared unto thee in the way as thou camest, hath sent me, that thou mightest receive thy sight, and be filled with the Holy Ghost.
18 And immediately there fell from his eyes as it had been scales: and he received sight forthwith, and arose, and was baptized.
The disciple Ananias put his hands on Paul and he received his sight. Then Paul got up and WAS WATER BAPTIZED after that. This all happened to the praying Paul who no doubt repented of his sins and asked for forgiveness.
Acts 22:16 And now what are you waiting for? Get up, be baptized and wash your sins away, calling on his name.'
When Paul had his vision restored to him, he was told to get up, be baptized and wash his sins away, calling on the Lord.
When people were baptized with water that was symbolic of having their sins washed away, after they repented.
In addition, people came out of the water after repenting and being baptized, they called upon the name of the Lord.
We are told to believe, and repent, and to call upon the name of the Lord.