i don't see fitness plus tab in my fitness app. I have only summary and sharing in bottom band.

You require ios13.4 and watchos7.2 and you need to be in one of the supported countries.

You require ios13.4 software version on your phone the fitness+ app is installed automatically here;

Are you in one of these countries?;

Australia, Canada, Ireland, New Zealand, the UK, or the US.

On your phone, go to Settings>General>Language & Region and, regardless of what it currently shows, re-select your region as the U.S.

Also, try unpairing and re-pairing your watch.

Sorry, that's all I've got. Hopefully, someone else will stop by with other suggestions.