The image shows a popular oven-cleaning trick that uses steam to soften baked-on grease and food residue. The basic idea is simple: place an oven-safe dish filled with water inside a warm oven, allow steam to build up, then wipe the loosened grime away once everything has cooled.

Some viral versions add a dishwasher tablet to the water. Although detergent may help dissolve grease, it is safer to avoid heating cleaning chemicals unless both the product label and your oven manufacturer specifically approve that use. Dishwasher tablets are designed for dishwashers, not for releasing detergent inside an oven.

A safer version uses plain water. Remove loose crumbs first, place an oven-safe dish containing water inside, and follow the steam-cleaning directions in your appliance manual. Some ovens have a dedicated steam-clean cycle that uses only about a cup of water. Afterward, let the oven cool completely before wiping the interior with a soft cloth.
Steam cleaning works best on fresh spills and light grease. Thick, burned-on residue may still require gentle scrubbing or a cleaner approved for your oven’s interior. Never mix cleaning products, and avoid abrasive tools that could damage the coating.

So Nana’s steam trick has a useful principle behind it, but the safest method is water, patience, and the manufacturer’s instructions—not an unidentified tablet heated inside the oven.