So, first thing you have to do is put it OUTSIDE!!!. There is not one plant or tree in the world that normally lives indoors... Some tropical plants can survive a houseplant indoors, but your rowan is not , so outside it is ( it WILL DIE indoors). Give it some time to adjust again: shade, then some morning sun, morning and evening, then all the way.
Second, it looks like it is planted in an ordinary mug.That means that there is probably no hole underneath for drainage.So, your little rowan will have wet feet, and probably DIE from that....(if there is a hole , forget what i said). Solution: repot asap.( and the p means: depending on your knowledge, season, ...)
Contrary to what many think: bonsai are not made by placing a young tree in a little pot, its quite the opposite really.
O and cut away the berries, your plant already has problems, and doesnt need to put its energy in reproduction...
So, if you really want to start with bonsai: keep this one alive( that is learn to water properly ), maybe repot as you can ( depending on the hole), and start to study; the basics will keep you busy for a few years...