HOW CAN I UPDATE ONLY SAFARI FROM MACOS SIERRA VERSIO 10.12.6 (16G2136) ?

You can't The way Safari is updated is by upgrading or updating your computer's software. An upgrade is when you install a newer OS version, such as upgrading from Catalina to Big Sur. An update is to install a newer version of the same operating system. The reason for this is because Safari is installed as part of the operating system. It cannot normally be individually installed. Incidentally, a newer version of Safari does not always work with every web site. Sometimes it is necessary to install another browser such as Firefox or one of the many browsers available from the Apple App Store to use with certain web sites. They are individually installed and upgraded.

There is a security update available for macOS Safari High Sierra.

About the security content of Security Update 2020-006 High Sierra, Security Update 2020-006 Mojave - Apple Support