I need to do root certificate

I requested that the hosting service install my Cloudflare certificate and they asked me to do so:

“root certificate that goes along with the CRT so that the site works perfectly.”

How to solve this problem?

Try this one:
https://support.cloudflare.com/hc/en-us/articles/218689638-What-are-the-root-certificate-authorities-CAs-used-with-Cloudflare-Origin-CA-