No reason for you to get stressed. The instructor/examiner will see what is going on. Leave them to do their job, and you concentrate on doing the best you can.

I had this situation when I did my A330 type rating. The guy in the left hand seat kept freezing up at the controls and panicking.
On several occasions, I had to say "I have control and communications" because he was making such a hash of things.

Part way through the final sim check, the examiner stopped the simulator and told the captain that I was having to flying single pilot operations in an A330 because the captain was so incompetent. The examiner actually apologized to me for having been put in this situation.

Cut a long story short, I got heaps of praise from the examiner during the de-brief, and the captain got suspended.

Truth be told, this is probably a good learning curve for you. Unfortunately, you are going to come across the occasional pilot like this on the line.