I did flooring for 5 years.
you might try a 4" razor scraper blade or dull putty knife turned around to the dull side & sanded grout.
use proper safety; gloves ,goggles, air respirator & ventilation .
Sprinkle the sanded grout then lightly scrape the gooooo the grout give the gooooo something to stick to.
Oh yea a lot of elbow grease & light pressure.