To update your nameservers at BlueHost and have your domain point to Skystra, please follow the below steps.
1. Login to your BlueHost Control Panel.
2. Select the Domain option at the top of the page.
3. Find the domain name and click the Name Servers tab.
4. Select the Use Custom Nameservers option, and input following nameservers into the appropriate fields:
5. Click the Save Nameserver Settings 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.