Theme app extension not working in older themes

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I have built an app extension, it is working fine in Online store 2.0 themes, but the themes which are no compatible, and the themes which are edited by merchant, and are not compatible to upgrade, How can I give them the features.

I am building a review rating app, but the store themes which are not 2.0 enabled, How can I embed the application widget inside the product page,

Please someone help me in this