Welcome! Yes, communication is a tough issue with our BPD adult child. Please take a look around this website. Here is a link from this website for you to take a look at called SET:
https://bpdfamily.com/message_board/index.php?topic=143695.0The main thing to remember is not to be hard on yourself, because these don't "take" over night with the BPD adult child and it takes a lot of practice and it may work for some issues but not others.
In addition I suggest you read up as much as you can about BPD. There is a book suggestion list in the library here. One book" Stop Walking on Eggshells" is a popular one here. It gives the caretakers permission to take care of themselves first . You are as important as your BPD child, and that often gets lost in the shuffle and struggle of day to day living with them.