What can I do for bad breath after removal of tonsils?

Decrease bacteria level. If the bad breath is coming from plaque buildup and bacteria buildup you need to use a tongue scraper and brush and floss your teeth to keep the bacteria level down.
Temporary. After throat or oral surgery, your breath will be really nasty until the worst of the exudate from the healing is resolved. You can scrape off the worst of it with dental floss, a scraper, or even try a toothbrush. Try not to damage the operative site. Good luck, and speedy recovery.