You must add it on HTML, try editing your product page: Themes > edit code > product template
Which theme are you using? We can customize it for you if you send us an Email with your Shopify store URL like mystore.myshopify.com then we will send you an invitation to your Shopify as a collaborator.
It depends what is "easy" for you :)
The simplest solution for me would be to add a line of code in your product template.
The simpler one, which would require more manual work, but no code editing would be to add a link to the "personal shopping request" page to the top of your product description. The link/button won't appear exactly where you want it, but you'll have it on the page.
Are you comfortable editing your theme's code?
Edit: I could help, too. Email me at firstname.lastname@example.org
Well, here is a rough draft:
Highlighted you'll see the code that you need to add:
<a href="/link-to-product-assist" class="btn product-form__cart-submit btn--secondary-accent">Personal Shopping Request</a>
Keep the class the same to get the "add to cart" button look. Change the contents of the href to your typeform.
How to find where to put that code?
search for <button type="submit" name="add" in your product theme