When you pray in tongues, it’s your spirit that prays, even though the Holy Spirit is the One who grants you the language or utterance.
For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries (1Corinthians 14:2).
Praying in tongues transcends the realm of the mind or human understanding, because the language is divine. All you do is connect your vocal organs to your human spirit and the flow takes place. Speaking in tongues isn’t something you force out of your mouth or try to do; it’s the Holy Spirit that enables you to do it.
“For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.” (1 Corinthians 14:14)
The Holy Spirit gives the ability, you’re the one who have to open your mouth in faith and speak the words He generates in your spirit.