How to change the glue records?
If you are using the normal Cloudflare nameservers (Bob.ns.cloudflare.net etc.) you do not need glue.
If you are using custom nameservers in Cloudflare, you will find the IP addresses under the Custom Nameservers section on the dashboard. You need your registrar to add these to the parent zone.
If you are using Cloudflare Registrar with custom nameservers the glue is managed automatically.