aspx file cannot be found in project folder

aspx file cannot be found in project folder

I am working on asp.net. There is a page tested on my localhost. This
project is transferred to me by previous developer. The page is
"localhost:4472/TblQualClients/List.aspx" and it is working fine, but I
could not find this aspx file in any of my folders; and in another aspx
document, I found there is a pointing to this page, but it is shown as
"File 'TblQualClients/List.aspx' was not found".
Can anyone help with this? Thank you very much.