We need to add an extra select option for one of the shipping methods.
For example, if the client selects the shipping method: collect from the depot. then we need to have a dropdown option to list all depot addresses.
This is not the free collect option, so we can't use pick up as the solution.
Can we customise the checkout shipping page? I can't find the source code.
Editing or adjusting the Checkout, beyond what is possible using the Theme Editor, is not possible by the Theme Support team, Experts, or external developers, as this code is not made accessible for security purposes.
Since the Checkout is a secured page, the source code is not made available. This helps to ensure that the information for both the merchant and their customers remains safe at all times.
If merchants were able to access or make changes to the Checkout, Shopify wouldn't be able to be PCI compliant since the PCI council needs to review the Checkout when changes are made to approve it.
There are some options available within the Theme Editor for customizing the Checkout, which can be accessed by going to Themes > Customize theme > Checkout. Nothing can be manually adjusted beyond that.
If there is anything else I can help you with, please let me know.