To create flow for low in stock you need to first follow these easy steps :
1. Go to General Settings
2. Click on email reminder settings and
3. Enable the Price drop button as shown in the screenshot by default its “no” to enable it click “yes”

To create the flow please watch this short video for better understanding (note please refresh the flows settings once saved):
To create your own flow for email reminders you can follow these steps :
1.First login to klaviyo
2. Go to “Flows”
Pro Tip: If you are not seeing Wishlist Guru – Price Drop in your “your metrics” section this is because klaviyo will not display flow triggers until they have received at least one event.Do this by triggering the event yourself. Try logging in to your store again and add one product to your wishlist to record this event on Klaviyo . Then you can check that in “your metrics” section that event will be displayed or added after that.