Repeat this to yourself: I’ve done this type of role before. I’ve prepared my answers.
you are qualified for this and ready
feeling nerves is normal, all humans do. The nerves can help you ace this interview. You’re ready for action. Think of the nerves as charge or energy.
the interviewer has felt this before too because once they too sat in your seat
smile. they will start with small talk and you can go into that. Exchange a couple of pleasantries at the beginning: comment on the building, the company, an event they’re doing etc
its okay to admit to the nerves in a casual way. You don’t have to be superhuman.
if you feel flustered take a breath, take a sip of water and take a moment before you answer.
you could always ask them to repeat the question or rephrase the question yourself if you feel you need time.
in case you feel going blank you can even admit to that and move on to the next question
direct your attention away from yourself (what did I just say? How do I sit? How do I look etc) and focus squarely on the other person
ask them questions
go slow
and breathe. Focus on the out breath, it’s calming
picture yourself smashing the interview
you got this!