Dallas here from the Shopify Social Care Team.
I would love to help you, but I will need a bit more context. You're wanting "até 1x de R$16.95 sem juros" to be located right under the product image correct?
Are you wanting it to look like the image that I am sharing?
May I ask what theme you're using?
Ok, I can definitely see if this is something that our themes team can get done for you. Are you able to share your store URL? In order to be sure this is something that they can get done for your under your free theme customization time, I will need to share a store URL so they can take a look. If you're able to give a URL that leads directly to where you want the customization that would be great!
If you would prefer to not use the Shopify design time for this then you could also reach out to the Shopify Experts who are very talented when it comes to major and minor customizations for Shopify stores.
Please let me know what you would prefer and if you do choose for us to look into Shopify design time first then please just send over the URL.