I have never been singing in a choir before. Yesterday I went to a organist for an audition. He asked me to sing the the tenor line while he was playing the full SATB arrangement. It felt a bit weird to not sing the highest line, ie the soprano line. It seem like it is easier to focus on the highest note. What do people do in order to hear and focus on the tenor line?
It was not the best plan to go to an organist without preparation and some attempts like I'm going to tell you here, if you want to avoid the risk to feel blamed again.
It was not bad when you heard also the soprano. The best will be if you would try before to go to an organist to listen in a 4 part setting at all voices and sing all one by one and finally pick out the tenor. There are many sites with choral music where you can listen at each voice isolated. Try also to focus first on the bass and then on the tenor.
As it always is with questions like this, the answer is lots of practice.
It sounds like you were being tested on sight-singing, which if you have no choral experience it makes sense that you weren't able to do it. The Tenor part is the hardest to sight sing (in my opinion and experience) since the soprano and bass lines are dominating and the alto has more obvious harmonies a lot of the time. You need to become adept at finding your starting pitch and moving to the correct notes based on the intervals in the music.