First, I’ll suggest checking this article here provided by WordPress themselves:
In there they’ll provide information on how you can change your Home and Site URL.
If After you updated the Home and Site URLs from the WordPress admin panel and you still can’t open the website with your new domain, then you can take the next step and update all the references for the Old Domain in your database as well.
Note:Please before you proceed take a snapshot of the droplet and also create a backup of the site (both files and database). This will ensure that if something goes wrong you can easily restore your site or droplet if needed
There are few ways to update the references in your database and it’s totally up to you which one you’ll choose. You can either change them manually if they’re not many or use an automation tool like a plugin or an external app.
One of the external apps that I’ve used and I know for sure that it’s working okay is: https://interconnectit.com/products/search-and-replace-for-wordpress-
You need to upload the script in your public_html folder and access in your browser, then you’ll need to fill in your database details and enter the old domain name and the domain name you want to use. Then you can first use the dry-run option and if there are references that need to be updated you can then run the script and update them.
Also, an alternative way is to use a plugin called “Duplicator” it will update all of the paths and references from the dev domain to the main domain. This is why we usually recommend using a plugin called: Duplicator. The plugin will generate a backup for your website’s files and database. Then when you import the files to the new domain, all of the references for the old domain name will be updated properly with the correct ones.
Another option is to use the All-in-One WP Migration plugin. The plugin will do the replacement for you during import. You do not need to use any additional database search and replace