Amend the soil. Learn how to prune. Loosen the ties around the stake.

thin the fruit just after flowering. If you truly want to keep it, better start reading.

Much too close to the fence unless you intend to train as an espalier.

To encourage growth, it'd be a good idea to prune away all the fruit and let the tree grow, it'll pay off in the out years. Out here in Cali, if you let the fruit trees produce too early, they will not grow to their full potential, or will at least take a lot longer to do so. There is a lot of info on pruning apple trees out there, just do a search.

Maybe we need another opinion to further confuse the OP. jemict, It would be very very beneficial to know where you are located and what you soil is like. Without that, advise given here is pretty worthless. It is soooo important to know where you are.

Soil seems fine by just looking at the tree.

Located in the UK.

In which case ..... Remove the green string. Remove the bamboo. Remove the suckers from the base of the trunk. Don't dig round it, just weed by hand. And then leave it alone for at least another year. Meanwhile find a book or website that discusses apple care in the UK. Pests, diseases, weather and pruning timing are all location specific. Apple growing in the UK

Seeing that your Hydrangea is blue and that you have a healthy heather there I am assuming you are somewhere with slightly acidic soil. Cornwall? Wales? Scotland? But it probably won't make much difference to your apple.