One effective method is placing some laundry scent beads, such as Downy Unstopables, into the vacuum bag. Just 10-12 beads can impart a fresh scent that will last for weeks.
Alternatively, adding a few drops of essential oils to a cotton ball or to a tablespoon of baking soda, and then dropping it into the vacuum bag, can have a similar effect.
For optimal results with these hacks, it's crucial to begin with a thoroughly cleaned vacuum and ensure proper ventilation by keeping doors and windows open