One effective way to remove dried primer from tiles is to use a razor blade or a scraper tool. Gently slide the blade or scraper along the surface of the tile at a shallow angle, being careful not to scratch the tile. The dried primer should start to come off in flakes or small pieces. Make sure to keep the blade or scraper flat against the tile to avoid any damage.
Alternatively, you can try using a mixture of warm water and dish soap. Apply this mixture to the dried primer and let it sit for a few minutes to soften the primer. Then, use a scrubbing pad or a soft brush to gently scrub away the primer. Rinse the tile thoroughly with clean water afterward.
Always test any method on a small, inconspicuous area of the tile first to ensure it doesn't cause any damage or discoloration.