Скорее может даже не удалить, а просто что б синхронизация тренировок обновилась 

Ciao ​@Evgeniy96. As far as I understand translating your request do you need to stop syncing your device with strava and delete your past activities?

Так. 

Ciao. Ok you can do it from your profile selecting the menu on the upper right part.

Then select "manage devices", it should be the third option... flag off what you need.

I hope it will help you

Немножко не то. Мне надо удалить загруженные тренировки Strava в Google Fit

So you're referring to google fit features. If so I can't help you. I could just advise to delete the connection between strava and google fit and then delete the workouts. Sorry to have not been able to help you.