If you have never been baptized in the Holy Spirit you can pray this prayer:

"Dear Heavenly Father, I am your child, and you said in your Word, 'If you then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him?" (Luke 11:13). So now I am asking you to fill me with the Holy Spirit. Holy Spirit, rise up within me as I praise God. I fully expect to speak with other tongues as You give me the utterance (Acts 2:4). In Jesus' Name, Amen!"

Now begin to praise God for filling you with the Holy Spirit. Speak those words and syllables you receive in your heart and mind, not in your own language but in a strange language, the language given to you by the Holy Spirit.  You have to use your own voice and activate it by faith.  God will not force you to speak.  Don't be concerned with how it sounds, because it is your heavenly language!  Then continue to pray in tongues every day!