The following are the steps To Create A Child Theme For AMP ( to override a file of AMP ).
Create a folder name “ampforwp” in your theme which you are currently using.
e.g: if you are using twenty seventeen theme then you have to create ampforwp folder in the twenty seventeen theme folder
The directory will look like
Add the file which you want to override in this folder.
For example: If you want to override single.php add your single.php in this folder and it will override the single.php of your AMP. ( Suppose you have Design-2 then this file will override the single.php of Design-2).
Similarly, you can override any file you want.
You can even override files according to post type and taxonomy. For more details Check here.