This is the link to the subcategory. I need to show 1 image per row instead of 2 or 3.
You can reach this URL by
https://tanyagoel.com/tg -------- Mechanisms
In this case, I am afraid we cannot rely only on custom CSS for the customization because the layout is also calculated in the other code of the theme (the layout is finalized based on the image dimensions on each row in the grid.)
You would need to manually customize the theme code in order to change its default grid layout, unfortunately. If you are not familiar with coding, I would recommend finding a freelancer to help you out in this case. You can find some great services at https://studio.envato.com/explore/wordpress-customization
The client is not going to pay for the customization. As you have developed the theme, you should be able to help.
The custom modification of the styles and/or functionality for your clients would be beyond our general support which includes only bug fixes or any support or update that are related to the default use of the theme.
We can only provide some minor adjustments (as provided in your other tickets); other than that, I am afraid you would need to manually customize it.
For more information about the support policy, please see: https://themeforest.net/page/item_support_policy