After you become a Christian, you have the right to ask your heavenly Father for the gift of the Holy Spirit:
"On one occasion, while he was eating with them, he gave them this command: "Do not leave Jerusalem, but wait for the gift my Father promised, which you have heard me speak about. For John baptized with water, but in a few days you will be baptized with the Holy Spirit."" (Acts 1:4-5)
"If you then, though you are evil, know how to give good gifts to your children, how much more will your Father in heaven give the Holy Spirit to those who ask him!" (Luke 11:13)
Notice what Luke 11:13 (above) says about how to receive the gift of the baptism of the Holy Spirit: We simply need to ask for it! Remember, we don't receive salvation by asking for the gift of the Holy Spirit, so Luke 11:13 (above) is not talking about receiving salvation. It's talking about receiving the gift of the baptism of the Holy Spirit (Acts 1:4-5, above).
So if you are a Christian, you can ask for the baptism of the Holy Spirit. Jesus is the One who baptizes us with the Holy Spirit (e.g. Mark 1:8), so why not ask Him to do that right now? Remember, you are asking Jesus for the promised gift of the power of the Holy Spirit for living the victorious life and for doing the things that God calls you to do for the glory of Jesus. Speaking in tongues is the
result of receiving the power of the Holy Spirit, it is not the goal.
Just as you received salvation by faith, you also receive the baptism of the Holy Spirit by faith. When you ask Jesus to do this for you, believe in faith that you have received it (just as you believe in faith that you have received salvation).