To update your nameservers at HostGator and have your domain point to Skystra, please follow the below steps.
1. Login to your HostGator Portal.
2. Select the Domains tab from the left-side menu.
3. Click the domain name to show the Domain Overview window.
4. Hover your mouse over the icons on the left side to expand them, and click on the Name Servers option.
5. Select the Manually set my name servers option, and input Skystra nameservers:
6. Click the Save Name Servers button 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.