To update nameservers for your domain registered with Skystra, log in to your AccountCenter, and click My Domains under the Domains section in the left frame:
Next, click on the three dots next to your domain, and select Manage Nameservers:
Use Custom Nameservers
Select Use custom nameservers (enter below) option:
Put in your custom nameservers in the Nameserver fields, and click Change Nameservers to save changes:
It can take up to 24 hours for the DNS changes to propagate (DNS propagation is the process of updating every server across the internet with new information) globally.
You can use whatsmydns to track the progress of the DNS propagation for your domain.