Hi! I think confidence depends on many things. Confidence grows when one is expert in their fields. Without knowing the basics one can not be confident at all. Before start a new job one should research about his job. If he knows about the fundamental knowledge of the job he will be confident.
One can make his confidence high in many ways. Reading newspaper helps to learn many things. Geographical, political, financial, regional or international lot of knowledge one can get by reading newspaper. For any job now a days basic general knowledge is need. Through internet

one can also gather a vast knowledge. For a better confidence developing computer skill is must. In the new era of artificial intelligence, learning AI will also help to grow more confidence.
If I got a job just got in a role I have never been in before I will try to make a good relationship with other staff. With the help of them I will learn my work so that I can do my duty. I will try to learn from internet also.
I think this is not necessary to be confident always. But if one always try to learn new things and try to adopt new skill he can grow confidence quickly. It is a common fact that a person will feel nervous in any new job. An experienced person generally does’t feel nervous in a new workplace. So a new employee should take suggestions from an experienced person. It will make him more confident and will increase self reliance.