You can get the seeds to grow your lanzone tree from the flesh of the fruit. Find a lanzone tree that already grows good tasting fruit. Split open the fruit and extract the largest green seeds within the pulp of the fruit. It's best to plant the seeds as soon as you extract them from the fruit. They will not germinate if you wait longer than eight days. You can also buy the seeds at a gardening store or online. The seed will likely have a sticky substance around it called mucilage. To remove the substance, run the seeds under cold water from your faucet. If you purchase the seeds from the store this substance will already be removed. Dig small holes about 1 cm (.4 inch) deep, put the seeds in the holes and cover the seeds with soil. You can do this in an indoor planter with good water drainage. Sandy loam that has a lot of organic material and is slightly acidic to neutral is the best kind of soil that you can use. It's a good idea to plant multiple langsat seeds just in case some of them don't germinate. Young seeds require a considerable amount of sunlight in order to germinate. If you are growing indoors, set your light timer to give your seeds 15 hours of light per day, or place your seed beds in a window facing south. After you plant your seeds, water them with a watering can. Make sure that you return to the seeds every day and keep the soil moist, but not flooded. You can check the moisture in the soil by putting your finger into it and checking if the soil under the surface is dry. In around 2-3 weeks, you should start to see your seeds germinate and grow small stalks. These seedlings will take about 10-18 months before they can be planted outside. When growing lanzone trees from seeds, it could take anywhere between 10-30 years or more for them to bear fruit.

Summary:
Get your seeds from healthy trees with large fruit. Rinse the seeds off. Plant the seeds in sandy loam, 3-5 cm (1-2 inches) apart. Keep the planted seeds in sunlight for 15 hours a day. Water the planted seeds every day. Wait 2-3 weeks for the seeds to germinate.