It is customary to translate the cohortative as "Let's" or "let me", but in Psalm 104, 33 (אשירה ליהוה בחיי אזמרה לאלהי בעודי) what does it mean? I think it simply translates as the future: I will sing as long as I exist.
Don't confuse how you translate it with its actual meaning. Let's/let me is a way to announce your intention to do something. Announcing your intention to do something is the meaning of the cohortative. That's what it means here too, even if you choose to use different words to translate it.