low confidence and anxiety/nerviousness

SWIM usually has very low confidence and nerviousness and SWIM alot of the time avoids talkign to people.
BUt SWIM is going to be joining a band that he is really dedcidated to doing his vocals.
SWIM knows hes good but once his low confidence and anxiety kicks in. He is afraid it will screw him up.
ARe there are things SWIM can take to either to calm his nerves or increase confidence.
SWIM is thinking about weed or low dose of alcohal or even dex.

SWIM has even heard little things like vitamin b or fish oil works. But for SWIMs nerves it is not good enough

Please help thanks!!