If you’ve never done it, then it can be quite difficult.
It may feel like you’re doing something wrong.
However, you aren’t.
Not wanting to talk isn’t a bad thing.
If you don’t feel like talking then just say ‘Hey, I don’t feel like talking right now. I’ll let you know when I’m up for it.’
That should be the end of the conversation.
If it isn’t, and that person starts to badger you, then you might have an entirely different problem on your hands.