How to auto-update stock quantity for product variations?

[GLHVending]

Hello

I have one product that has variations (colors).  When i change the variant from the drop down it does not auto update the stock quantity.  Ie.  It starts with blue and shows 5 avail.  I select green and it shows 5 avail. (i have actually only have 4 in stock).  That quantity avail doesn't change until i hit refresh.  similarly if i select orange (i have non in stock) it will still say 5 in stock but the button will now say sold out. very confusing for customers. I am using Simple Theme version 12.6.1 and that is the cause for the issue.  Is there code i can add to fix this or is it time to change my theme?  i just really like the layout of the simple theme.  link to problem area below.  TIA

https://krazytown.ca/products/flat-top-tomy