Black magic has traditionally referred to the use of supernatural powers or magic for evil and selfish purposes.
Simply by 1. reciting Quranic verses like Ayatul Kursi and Suras like Sura al-Falaq and Sura Annaas. 2. Also by reciting Du'a and supplications for protection from harm. 3. It is also very useful to pay daily Sadaqa for protection from every harm. 4. No doubt, seeking the Waseela of Ahlul Bayt (AS) is always useful.
It is not permissible to seek help of Jinns through black magic to harm other persons. Allah (SWT) says in Quran (And some men were seeking help from some Jinns but the Jinns added on their difficulties)Sura Al-Jinn, Verse 6. This means that seeking help of Jinns is bad and harmful.
Harming others through any way is also a sinful act. So, the aim of harming others is out of Muslim morals and the mean of Jinns is also bad.
However it is good to avoid being paranoid about jinns or black magic. Most jinns have better things to do than get involved in people's lives, and some people blame everything on jinns or black magic because it is easier or less painful than looking at some of the tangible and obvious reasons for why they are having problems.
Of course, if someone genuinely feels they are having a problem in this area, it should be dealt with the same as one would deal with any other life problem.
First question is : How can you prove that the item is associated to black magic only and has nothing to do with other purposes like any other item?
Second question: Do you know for sure the owner of the item or not? If you know the owner of the item, then you must give it to him/her. If you do not know the owner and there is no considerable value for it, then you can throw it away provided that there is no possibility to know the owner.
Protection from black magic is by reciting Sura Falaq and Sura An Naas and Ayatul Kursi along with Du'a and Sadaqa.
Reciting Qur'an regularly and saying the 5 daily prayers helps.
If you feel like you are genuinely "off" and there is no reason why you are feeling strange, or if things are frequently going wrong and there is no logical reason for them to go wrong, or if you see/hear unusual and disturbing things around you, or if you have dreams about disturbing things for no logical reason (such as stress) and this is not normal for you, or if you have some sort of evidence that someone may have been doing things to you, you could consult a scholar who has experience in these matters and ask them to look into it for you.
However, it is also good to look for other explanations first, because sometimes just believing that someone has done something to us causes us to subconsciously sabotage ourselves and it becomes a self-fulfilling prophecy!