Create A FOMO Using Conversion Plus: Shopify App Review and Tutorial

Once the app is installed, you should be on the general settings page. The first step is to enable the countdown timer, 
The next section is basically an ad for another app by the same developer, and you can skip that part. 
Now it is time to choose for how long your cart is going to be reserved. You can choose from 1 to 360 minutes. We advise going with 30 minutes or more. 
Next in line is a countdown text. The Premade text is “Your cart is reserved for {{time_remaining}} minutes!”, this is ok, but you should go with something more personal, unique to your brand, so be sure to edit it.
When the countdown expires, you can also edit the text and add <a> and <i> HTML tags in your countdown timer message, which can be very useful.
Moving to the next field, where you need to choose if you want to clear the cart after the countdown expires. Before making your decision, be sure to contact your marketing team. 
The last step in this general settings page is customization. At the bottom of the page, you should see a preview of the countdown widget. Customization is also limited, so you can only change colors and sizes. For the background color, you can choose some light shade of gray and border-colour some darker gray. You can also go on to edit the font color is ok, and font size.
In case you want to actually hold the items once added to the cart, then you will need to upgrade to the bronze plan. The inventory hold will only last as long as the duration of the cart reservation timer value you specified above.

Click on save and reload your store to see the changes you have made and test it out. Our test proved that the reservation countdown timer starts after the first product is added.
To uninstall the app from your store, first, uninstall the app from the admin; next, go to the theme code. Go to the Online Store sales channel here; just to be secure, first, make a copy of your current live theme. Click on Actions here and then Duplicate. Once the duplicate is made, you can proceed to the code editor.
Again click on actions, and now, from the drop-down list, click on edit code. 

This app is active on the cart page, so first check templates and then cart.liquid. Delete this line before {% comment %} and click on save. Scroll down to the snippets since there must be something left, and here it is, lick on vncpc.liquid, and in a new tab, just click on delete file. Save changes, and you are all set!