https://wccftech.com/apple-seeds-watchos-7-public-beta-for-testing-purposes/

Today, Apple has decided to seed the third beta of watchOS 7 to the public for testing purposes. The second public beta arrives a week after the second beta was released to the public and a few days after Apple released the third beta to developers. If you're a public beta tester, you can download and install beta 3 of watchOS 7 on your Apple Watch right now.

watchOS 7 beta 3 can be downloaded on your Apple Watch after you have installed the appropriate configuration profile from Apple's Public Beta website. Take note that since it is still a beta, you should not install it on your primary device. Moreover, you can not downgrade it to watchOS 6, so do proceed with precaution.