You mean Arnica. It’s a herb often recommended (in tablet or cream form from boots/ chemist) as it helps ease bruising and swelling. However, both arnica and garlic thin the blood and make it pass more easily through the blood vessels. This can put you at higher risk of heamorrage during your operation, or after, when your stitches are not yet healed. The risk is only small, but it is there nontheless.
Unless your surgeon recommends taking Arnica, don’t take it until 6+ weeks after your BA/ operation, when your scars have healed up.
You should be absolutely fine eating garlic in small amounts. It’s only really a problem when you’re taking lots of blood thinners at once xx