I started a new business in jan 2023. I completed a course for this is December 2022. Should I claim this now or next year?

Generally, you can’t claim expenses that you incurred before your business started as self-employment costs.

Also, if the training courses were to get new skills, then you can't claim them as self-employment expenses even if you took them after you started. 

However, you might be able to claim the course as a tuition amount if the fees are eligible.