A disciplinary meeting or hearing is your opportunity to put your side of the story forward.  You should be told before the meeting what the problem your employer wishes to discuss is. It's a good idea to prepare your responses in writing. You can ask your support person to speak for you. If you have any questions about what you are accused of doing you can ask them. You can ask to see the evidence or witness statements. You can provide your own evidence or witness statements to show your side of the story. Remain polite and calm.
https://youtu.be/iWgwTwS2lco