For creating the actual lead magnet "the thing" add this skill as .md to chatgpt.
It will learn what you sell, who you sell to, and generate the lead magnet idea.
After that you can use the chat/project for generating the actual lead magnet by giving it the prospects website:
"Build a lead magnet for X. Here's their site. Here's what they do {{briefly in own words as websites can be ambiguous at times}}