Your psychologist should definitely be working with you both to explore strategies that work for your young person. Each individual is different. However, co-regulation works much the same no matter the age. It’s about holding space, naming what you can visualise is occurring. Later once calm and appropriate discuss what’s hPpened and ask what could be different next time to keep building capacity.

Reading your question another time, I find it strange that his psychologist doesn’t offer co-regulation strategies & training.
A lot comes down to through your relationship you help your kids to regulate, which can be;
describe what you see
label emotions,
prompt to deep breathing exercise
yoga exercises
prompt to sit down and drink a sip of water
prompt to find a quiet spot
environmental factors for example dimmed light, soft music etc

Currently I look for my youngest into service provided by Brain Train https://www.thebraintrainco.com/
I don’t know where about you live ? And do you have NDIS funding for your teen ?