The wpmem_username_link_str filter hook allows you to change the text (and if desired, the link) of the forgot username link that shows in the main body login form.
Similar to wpmem_reg_link_str for the register page link and wpmem_forgot_link_str for the forgot password reset link.
(string) (required) The HTML of the forgot username string, includes the link and link text.
(string) (optional) The actual link (useful for making new text without having to extract the link).
Introduced in version 3.0.9
wpmem_forgot_link_str is located in forms.php