I’m new to plants and

I just got this tiny (I think burgundy?) rubber tree a week ago and I noticed one of the leaves are turning brown on the tip. I'm not sure if it was already there when I got the plant or if I've caused it. The plant is still in its original plastic pot and I haven’t changed the soil. I've just started to use a grow light at least 5 hours a day because I don’t get much sunlight where I live.

Should I replace the soil with fast draining soil???

What could I be doing wrong?