Are you using Lightsail DNS? If so, it's pretty easy, just create a DNS entry with the subdomain '*' and point it to your Lightsail instance or IP.
What have you tried? What errors have you encountered?
Lightsail support creating wildcard DNS record as specified here: https://lightsail.aws.amazon.com/ls/docs/en_us/articles/understanding-dns-in-amazon-lightsail. You can create DNS records like A/NS/etc on Lightsail web console, and pointing to the ip address or load balancer of your wordpress instance. Hope it helps!
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