Set Product Quantity page to be increments of 3

[JPM1]

I would like to set the Quantity drop-down menu to only show option '3' or increments of 3 (e.g., 3, 6, 9, 12, ....). I would also be okay with having a validation rule that informs the customer to select a value/increment of 3 on the product page. TLDR, I need Shopify to not allow customers to select single units. 

I tried to set up a Variant called Quantity, but the original/standard Quantity drop-down appears on the page preview.  

Any guidance would be appreciated, thank you! 

[Ahmad31]

Yes i can help you with this 

[nickemery]

To set the Quantity drop-down to show only increments of 3 in Shopify, you can achieve this by customizing your theme’s code or adding validation. Here are two approaches
Custom Code

In your theme's code, locate the product-template.liquid file and modify the quantity input to allow increments of 3 only. You can use JavaScript to set a step value on the quantity input, ensuring customers can only select 3, 6, 9, etc.
Try Using this Custom Code for Quantity Selector;
document.querySelector('input[name="quantity"]').setAttribute('step', 3);