Below are some Bible verses that portrays the phrase 'bless God':
First Instance:
And you shall eat and be full, and you shall bless the Lord your God for the good land he has given you. (Deuteronomy 8:10)
Explanation: Bless here means to thank God for all He has given you.
Second Instance:
Enter his gates with thanksgiving, and his courts with praise! Give thanks to him; bless his name! (Psalm 100:4).
All your works shall give thanks to you, O Lord, and all your saints shall bless you! (Psalm 145:10)
Bless the Lord, O my soul, and forget not all his benefits, (Psalm 103:2)
Sing to the Lord, bless his name; tell of his salvation from day to day. Declare his glory among the nations, his marvelous works among all the peoples! (Psalm 96:2-3)
Explanation: Bless here means to announce all the good things about
God in a joyful way.
Third Instance:
Bless the Lord, O my soul! O Lord my God, you are very great! You are clothed with splendor and majesty, (Psalm 104:1)
Explanation: Bless here means acknowledging how great God is.
Fourth Instance:
Therefore David blessed the Lord in the presence of all the assembly. And David said: "Blessed are you, O Lord, the God of Israel our father, forever and ever." (1 Chronicles 29:10)
Explanation: Bless here means acknowledging that God is Himself blessed.
Question: Can Man Bless God While Praying?
Answer: Yes