Remove the affiliate registration form from the Affiliate Area page
By default, when the Allow Affiliate Registration option is enabled in AffiliateWP's settings (Affiliates → Settings → Misc), an affiliate registration form and an affiliate login form will appear on the page you have created for your Affiliate Area (i.e. yoursite.com/affiliate-area).
You may want to keep the affiliate login form visible on the affiliate area page, but place the affiliate registration form on another page on your website using the [affiliate_registration] shortcode. This can be done by simply going to the Affiliate Form Settings - Affiliate Area Forms section in Affiliates → Settings → General, and change your selection to only display the affiliate login form.