When we don't know how to pray, all we need to do is ask the Holy Spirit to pray for us and He will! for He knows our hearts and what is in our hearts.
"The Spirit too comes to help us in our weakness. For when we cannot choose words in order to pray properly. the Spirit expresses our plea in a way that could never be put into words, and God who knows everything in our hearts knows perfectly well what he means, and that pleas of the saints expressed by the Spirit are according to the mind of God" Romans 8:26-27