In API integration, I only got GET APIs, where can I get the API to perform CRUD (create, read, update, delete) operations?

I’m sorry, but right now the only API avaliable for OJS is the one they suggested you in this thread:

And as you noticed this is still not complete:
https://docs.pkp.sfu.ca/dev/api

Please keep talking in the first thread to keep the convesation sorted.