Subdomain redirection to EC2 instance

Hi, I am new to DNS and server setup. I have a website - abc.com hosted in hostgator and a python application running in ec2 instance. I need to point app.abc.com to the ec2 the instance while keeping the abc.com as it is.

What I have tried:
I have already created an elastic IP. Created nameserver records in Route 53 and added 4 NS in hostgator. Then, I created app.abc.com record in route 53. As of now, app.abc.com is redirecting to the ec2 instance but abc.com is not working. Im guessing I should not have added the 4 NS records from route 53 to the hostgator's DNS records.

Any idea on how to implement this?