If you are not at Mass (e.g., at a concert, at a group prayer, etc.), then you may say Alleluia.* If you are at Mass, then you may not say Alleluia even if it is in a song or hymn such as you might use for the entrance, offertory, or Communion. Thus, if you are singing a worship song at Mass, it may not include the word Alleluia.
Was that what you were asking?
*As I understand it, the prohibition against the Alleluia would also extend to the Liturgy of the Hours and other liturgical actions like baptisms or weddings performed outside of Mass, though I’m not positive and it is not relevant here.