You can add these records yourself. Open your domain at https://railway.com/workspace/domains, and you'll see a DNS records table for it. Add a record, pick the type (MX, TXT, CNAME, etc.), enter the name and value from your provider, and save. DNS changes usually propagate within a few minutes.

You're on the right page. Click on one of your domain cards to open it, and the DNS records table will appear on the next screen where you can add your records.