In order to integrate VWO Engage(formerly PushCrew) on your BigCommerce website page wise(i.e on specific pages), follow the steps mentioned below:
1. Log into your BigCommerce dashboard.
2. Click on Storefront on the left side of the panel.
3. Select Footer Scripts from the left side.
4. Paste the SmartCode in the Footer section and save the code to get opt-in on your BigCommerce website page.
In order to get the VWO Engage SmartCode, kindly visit this link on your VWO Engage dashboard. 
You can preview the changes made to the website page by clicking 'View Store' option in the top left corner. Publish the changes to the website.
If the code is placed correctly, you will be able to see the Opt-in on the website page as shown in the below screenshot. 