The simplest way is to actually emulate the way a tombola / lottery draw machine works.
It has a container which holds all the numbers in the competition, and rotates un=til one drops out.
So create a List(Of Integer) and fill it with all the numbers you can have. If there are 10 "balls" in play, put the numbers 1 to 10 in there.
Then generate a random number in the collection - use the Random class to select a number between 0 and the number of items in the List minus one, then use that as an index into teh List. That value will be your "winner".
Then in your timer, you generate another random number oto access an item from the List, get the value, and remove it from what is left in the collection.
If that matches your winner, it's over. If not, let the Timer tick again.
It's not difficult, not really - it's the way you would do it manually!
If you are having problems getting started at all, then this may help:
How to Write Code to Solve a Problem, A Beginner's Guide[
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