If your toilet is already over flooding, follow these steps to fix the issue:
: Over time, calcium or rust can block the rim feed and jet holes. Regular cleaning of these small holes can prevent a weak or incomplete flush. Flush Valve Maintenance
: Low water levels in the cistern can weaken the flush force. Ensure your refill tube is correctly positioned in the overflow pipe and the roller clamp is set to "8" for maximum flow. Mineral Buildup
If the tank isn't filling enough, the flush lacks the force to clear solids.