Thanks for the photo. Your container with drain holes that is good, but the soil that has been used maybe part of the problem. Should have used potting soil not garden soil. Garden soil tends to stay wet way longer than potting soil and is best used to be mixed in with outdoor in ground planting. Even with potting soil, I still add some more perlite or pumice to it, to make really airy at root zone to help the growth of the roots.
You can try and inspect the roots of your plant and see its condition. I don't give up on my plants when it is in stress like that, but start with the soil. If it were mine, I would repot and use a proper potting soil for it. Schefflera for the most part as it matures, goes quite drought tolerant, so it does not like to be staying too wet. It is a different scenario if it is planted as a landscape plant where its roots have much more space to move about, there it can endure nicely all the rain and humidity it can take.
