Currently I have a ELB (spun up using kubernetes service 'LoadBalancer') that points a certain port let's just say 8100 to a node-port on my instances for an application that I spun up using helm/kubernetes. I can access the UI fine by using the public_dns_elb:8100.
Is it possible to make a route53 dns record at say test-app.com and then get to the application by doing test-app.com:8100 in my browser?
No, that is not something browsers support. You must use ports 80 and 443 for the defaults.