If you want to add custom field in any schema properties for this follow below steps:
Step 1: Modify the schema where you want to add Custom field. You need to go to the WordPress Dashboard -> Structured Data -> Schema Types -> You need to edit any schema types.

Step 2: Which schema type you want to edit just you need to select Schema type.
Step 3: Check “Modify Schema Output” option

Step 4: In the first field, you need to “Select schema property” and the second field “Select Custom field” and the third field “Select post meta key” here is the list of post meta key as per your requirement you can search.
Step 5: If you want to add more field then click on the “Add Field” button.
Step 6: After that click on the “Update” button.
That’s it for this tutorial!
We hope it helped you. If you have any feedback or questions or do you want us to create compatibility for any other schema type which isn’t listed in our plugin then you can request us we will surely implement it as soon as possible.
Just contact us here and we are always available for you.