Is "topping up" oil healthy for my motorcycle?

I bought my first motorcycle around a week ago (2012 Yamaha V-Star 250). I need to change the oil, and my friends father is able to help me out with this around a week from now. I will need to ride my motorcycle before then, however it's oil level is below the minimum mark on the gauge. I have been to a Yamaha dealership to buy some oil, yet I'm not sure if it is the same as what the previous owner put in. I'll just put in around 400mls as it is all i can spare for now. I was just wondering if it is healthy for the motorcycle to simply "top up" the oil level without draining any if its only a weeks worth of riding ahead of me, and if so, is it okay to mix a small amount of oil left in the cycle from the previous owner with possibly different oil I have bought.Also if anyone has any links to a video explaining how to do this, do you mind sending it to me as I am very new to motorcycles and have literally no clue what I'm doing lol wish me luckThanks!! via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/exzlme/is_topping_up_oil_healthy_for_my_motorcycle/?utm_source=ifttt