Again and again, "Bless the Lord, Oh My Soul" comes up in scripture. Psalm 103, for example, which was our devotional reading this morning. This is a puzzle for many of us. How can we "Bless the Lord"? Are we capable of "handing out" graciousness to God? Does God needs a blessing from us? No of course not. God is the source of all blessings and doesn't NEED our blessing.
Consider it this way: As you become aware of God's blessing upon you, your whole self fills with gratitude. It is as if our soul itself begins to reflect the One who is the source of all Goodness.
Not sure that helps you - but when I try to wrap my mind around how I can bless God, I find it helpful to see my thankfulness as a reflection of God's blessing that points back to God in tribute and praise.