Hi @Rameshnathan 

1. If you are using AES and already have the CICD piplelines setup, then you should be able to submit your app and it would be installed in the QA instance.

2. Another way can be to publish your custom application in the app repo and pull the application in other instance.

3. Conventional way is to publish your application as a update set and retrieve in another instance, if other two options doesn't work for you.

More details can be odund here in SN support aprticle:

https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0961293