you wont get any more this year. the tree will flower in early spring and providing the weather is decent you will get more fruit next year.
make sure it doesn't dry out if we have little rain in autumn.
research its care by googling info from the RHS [Royal Horticultural Society

welcome to GoY too :o)

It will probably not fruit next year as it will be making good roots. Even if a few plums set its best not to allow them to grow, if you have the willpower!

Fruit trees may ripen fruits that have already set while they are in their containers, but they will usually spend the next two to three years growing roots and leaves.