What steps are needed to be able to manually export selected activities to Strava from Garmin Connect?

Garmin Connect » Activities » concerned Activity » cogwheel icon » Export File » unzip the file » Strava web » + icon top right » Upload Activity » File » Choose Files » upload the unzipped FIT file

I let all activities sync to Strava, but by default they are private. If i don't want a certain activity on my Strava Account I simply delete it. For the others I do changes e.g. name of the acitivity and set the required privacy level.