The first thing I would do is learn how to take care of this plant.
This is a Tiger Bark Ficus. It has higher water needs than most other bonsai and can tolerate being indoors, however it would much prefer to be outdoors as long as it is warm and sunny. When the weather starts cooling and starts to get below freezing at night, then bring it inside, ideally where it will still be cool, but not get below freezing, such as in a garage or enclosed patio.
For now, the soil looks very muddy underneath the topdressing (the rocks) and June to early July is a great time to repot this particular species (As long as you are in the Northern Hemisphere). For soil you will find much conflicting information on the best soil for this species. I am not an expert at all, let alone for this species, but many recommend a soil that is 50% Fir Bark and 50% Lava Rock. If you cannot find those anywhere near you, then you can use a fine orchid soil mix amended with ideally lava rock, but Perlite would suffice. The important part is that it is free draining but stays moist throughout the day.
Hopefully this helps!