Welcome to the forum and to RT ownership. The forum is great resource with good people. The bike will you appreciate more everytime go for a ride.
Oil questions always receive variing opinions on what you could not should not do. This is my $.02 worth. The engineers and mechanics I have spoken with do not recommend mixing oils. I am not inclined to mix oils unless circumstances absolutely require me to do so and then I do an oil and filter change as soon as possible.
Assuming the oil has been changed did the seller provide a service history to include receipt for the work. The oil type may be listed on the receipt or if the owners manual has the service stamp, see the back of the manual, you may be able to contact the service provider and ask and use that oil to top off the bike, if it is synthetic fine, if it is dino use the dino and you can change to synthetic at your next oil change.
Some options to consider. Since you are new to the bike are your sure your bike needs oil? Follow the owner's manual prescribed method for checking oil, which is for my 2011 that is with the engine hot and sitting off for 5 minutes and then check the level in the sight glass the 2010 will be the same. The level should be between the bottom and top of the circle in the sight glass.
If the service information is not available and you assume the bike has been serviced according to BMW's mainteance schedule it has been 3400 miles since the last oil change or if yuo do not knwo the service history you could change the oil and filter now. You now know what type of oil is in the bike and not have to worry about it anymore.
Sorry for the long post.
Chris