Inventory the records that matter
Review the current DNS zone before changing anything. Record the entries used by the website, mail, verification checks, and any other subdomains or services. Include less visible records such as TXT entries: they may support ownership checks or email policies even when they do not load a page in a browser.
Compare this inventory with the destination zone and confirm each required record has an equivalent there. Do not assume a new zone automatically discovers every service using the domain. If you are unsure why a record exists, identify its owner or purpose before deleting or replacing it.
Switch only after the destination is ready
Make sure the destination zone is active and its records have been reviewed before updating nameservers at the registrar. The registrar controls which nameservers are delegated for the domain; records in an unselected zone will not answer public DNS queries. Keep access to both the registrar and the destination DNS settings during the change.
After the update, check the domain and key subdomains from more than one network or resolver, and verify mail separately from website access. DNS caches can retain prior answers for a while, so a partial transition may not mean the new configuration is wrong. Avoid removing the old setup until the new records are serving the expected traffic.