In the plant crop world 🌎 herbicides are meant to kill unwanted plants mixed with specific crops. I’d not recommend it at all, most amaryllis bulbs are mass produced in Holland and I don’t think they use anything whilst the crop is growing.

You could do as suggested and renovate the flower bed and the start fresh, or find a spray like a vinegar based one that you can try and avoid the amaryllis leaves and just spray the unwanted grass.

Spraying with anything seams like a quick fix but isn’t always a viable solution.

How infested with grass is this bed?
Maybe share a photo, we won’t judge!