Depends on the reason. Is it below grade? Are there roots in the lines to a septic tank? Is the septic full? If there is anything in the line between the toilet and the street or septic, try cleaning it out with a snake. Or get someone with a power snake. If there are roots, get a root killer from the hardware store. If below grade, it needs a pump and something beyond my expertise and I’m guessing yours too. Ask a professional. Try the at home stuff first. Good luck.
If it is has a tank that holds water and not an on demand feed, the water level may be too low. http://www.home-repair-central.com/adjusting-the-toilet-tank-water-levels.html
Depends on the reason. Is it below grade? Are there roots in the lines to a septic tank? Is the septic full? If there is anything in the line between the toilet and the street or septic, try cleaning it out with a snake. Or get someone with a power snake. If there are roots, get a root killer from the hardware store. If below grade, it needs a pump and something beyond my expertise and I’m guessing yours too. Ask a professional. Try the at home stuff first. Good luck.