I think you need a domain to config the URL of the WordPress site. Below is the document how you can config the domains on Lightsail WordPress multisite.
I need some help about lightsail wordpress. Plz give me some advice!
Images cannot be displayed in my snapshot lightsail wordpress instance
how to configure AWS cloudfront/distribution for plesk Ubuntu based wordpress website on lightsail instanceasked 3 months ago
Adding HTTPS on a lightsail wordpress site.asked 12 days ago
how to post static files alongside wordpress installation that uses the same domain as the wordpress siteAccepted Answerasked 15 days ago
Can someone help me how to access to my wordpress again?asked 4 months ago
Migrate wordpress to lightsail please helpasked 8 months ago
Lightsail instance stops loading Wordpress site, requiring instance rebootasked 6 months ago
Default username for WordPress in LightSailAccepted Answerasked 6 months ago
Location of root path for wordpress on Lightsailasked 5 months ago