amazon web services - How to set reverse DNS in AWS for my private nameserver?

I wanted to set rDNS for AWS for my mail server. I have created glue records, therefore my nameservers are like ns1.mydomain.com & ns2.mydomain.com.
Note: My domain registrar is AWS and may mailserver will take care of DNS.

So, I followed this guide https://aws.amazon.com/premiumsupport/knowledge-center/route-53-reverse-dns/, but I am little confused.

Suppose my IP is 50.60.70.80.

I created a new hosted zone with the name 70.60.50.in-addr.arpa

I created a record set and added a PTR record for the SMTP server as follows
Name field : 80.70.60.50.in-addr.arpa
Value field: mail.mydomain.com

Now, in this hosted zone, I have 2 extra records.
In type NS, I replaced AWS nameservers to my nameservers ns1.mydomain.com & ns2.mydomain.com.
I don't know what to do with SOA. I would be thankful for any help.