You can just skip it or use liquid (though i'm not sure if it actually has less salt) or homemade beef stock, i think it adds to the recipe but it's not a key ingredient so to speak, that said i'm fairly certain that there's more salt in 7 tablespoons of soy sauce than there is in the whole cube by a considerable margin so if that's your concern i think i'd rather keep the cube and use low salt soy sauce instead.

Definitely use low salt soy sauce if salt is a concern regardless of what you do with the cube.

Also if you're cutting the salt i'd sub the sugar with mild or bitter honey, maybe something like chestnut honey.