There wasn’t an identifiable first apple or orange seed. They would have evolved from some preceding plant species slowly over time. So over thousands of generations the preceding plant becomes more and more like an apple or orange tree until eventually it matches what we would recognize as an apple or orange tree but there wasn’t a single point where you could say one generation wasn’t an apple or orange tree and the next was. Think of it like a person aging. Any given day they won’t look any different than the day before but look at two pictures taken 20 years apart and you will see how they aged.
> just like the What came first he chicken or egg debate
The egg came first, and was made by an animal that was almost, but not entirely a chicken. In a similar way the first “apple seed” came from the fruit of a tree that was almost, but not exactly an apple tree. Over millions of millions of years you can move from chickens to proto-chickens to ancient birds to where reptiles and birds split away from each other; and all of them are laying eggs.
Evolution also applies to plants. Each plant has offspring that are very very similar to itself genetically, but might have the tiniest bit of randomness thrown in. If that randomness is benefitial so that the offspring has more children or is better at surviving than it’s siblings, slowly that mutation will become more and more common. You can take an apple tree and move backwards and while each generation looks almost identical to the one before or after it, over a large enough distance you have very different looking trees, but both using seeds to make offspring.