Hi Robert,
If Windows 7 originally came preinstalled on the laptop, check for a Certificate of Authenticity (COA) sticker on the bottom of the laptop or inside the battery compartment. The Windows 7 product key may be printed there.
If you purchased Windows 7 separately, check the original packaging or purchase confirmation email. Microsoft generally cannot provide a replacement key if you no longer have the original product key or proof of purchase.
Also keep in mind that Windows 7 reached end of support on January 14, 2020, so if your laptop supports a newer version of Windows, I would recommend using a currently supported version instead.
Thank you, and feel free to respond back for more assistance.