Hello,
You will need to go to websites such as the Internet Archive to find Windows 7 ISOs, as Microsoft no longer supports Windows 7, 8, or 8.1.
Repositories such as https://archive.org/details/windows-7-home-prem-english should work. Make sure the version you download is the correct version for your activation key, otherwise, Windows will not activate.
A disclaimer: The website mentioned is a non-Microsoft website. This page appears to be providing accurate, safe information. Please watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it. In addition, as mentioned already, Windows 7 went out of support. Exercise caution when browsing the internet (or connecting to the internet in general) and be wary of suspicious apps and links.
I hope this information helps.