Welcome to forum.
If you have a disease problem the best move would be to start a thread and post pictures of the problem. Since you are new to the forum you may be limited in the number of pictures you can put in one post so it may take multiple posts to get all of the pictures up on the forum.
To aid people on the forum take multiple pictures of the disease in different stages and different perspectives. For example take pictures of leaves that have little, some and a lot of the disease present on the leaves. Take pictures of the back and front of the leaves. That helps a lot in disease identification. Also tell us the cultivar (Honeycrisp, Granny Smith, etc.) and the rootstock if known.
For guides on diseases here are some links that have pictures of diseases.
https://blogs.cornell.edu/plantpathhvl/apple-diseases/
Also do you spray your trees or bag your apples? To protect the fruit from insects you will need to do one or the other or both. To protect the leaves you either spray a fungicide or pick apple trees that are resistant to the diseases you have problems with.
Here is a organic spray schedule and a synthetic spray schedule that will give you some guidance on how to protect your trees.