Hi
Third-party apps
Some third-party apps offer the ability to receive Move goal credit (but not Exercise credit, due to programming / API limitations), on your watch, for workouts that are undertaken whilst the watch is not being worn.
Examples that you may wish to consider:
Fitmanual
Manual Move
Other such apps may be available in the App Store.
Add data manually
Data (including calories, steps and exercise minutes) cannot be added manually to the Activity app on your Apple Watch.
Workouts can be added manually to the Health app on your iPhone. This aggregates all health and activity data from your watch, iPhone and any other sources. However, note that this will not credit Active Calories or Exercise to your watch.
To add a workout, go to: Health Data (tab) > Activity > tap on Workouts > tap on the "+" sign (upper-right) > enter your workout data.
More information:
Use the Health app on your iPhone or iPod touch - Apple Support