Hello ​@Galih purnanda sakti and thank you for your post.

Can you check and see what version of Watch OS you have on your Apple Watch?  The Strava Watch app will no longer be available for any watchOS below watchOS 9. If you haven't updated your Watch to the recent OS, you can update your watchOS by going to:
 
Watch iOS app > General > Software Update
 
If your device cannot update to watchOS 9 or higher, you can still upload your activities to Strava using the Apple Watch's Workout app. Please review the directions below to set this up:
 

Connecting Strava and the Apple Health App

• From your profile, open Settings (gear icon) > Applications, Services, and Devices> Health > Select the plus sign icon.
• Tap Connect on the next screen.
• You'll be taken to the Health Access page where you can enable the sharing of data from Strava to Health. You can control which types of information Strava will read and write to Health. You must enable Workouts for the sharing of any data (cycling, running, calories, etc.) to work.
  • After the initial set up, you can modify Strava's Health Access by going into the Health app and clicking on Sources > Strava.

Syncing from Strava to Health

• Navigate to Settings (gear icon) > Applications, Services, and Devices > Health and toggle Send to Health ON.
• Strava will send data to Health such as route information, activity type, distance, time, and calories automatically. Please be aware that route information from third-party activities (Garmin, Zwift, etc.) will not sync to Health.

Syncing activities from the Workout app to Strava

• Navigate to Settings (gear icon) > Applications, Services, and Devices > Health > toggle Automatic Uploads ON. New activities recorded with the Workout app will now automatically sync to your Strava account.
• Alternatively, you can manually select activities to sync using the Import button next to any activities listed on that screen.
• If you see a warning that the workout does not have route information, and the activity is an indoor workout, select Import. If the activity is an outdoor workout select Maybe Later and try uploading again later.

 
You can also review our article on our Health integration.