Let's get to it right away!

1. Press Win + R. That'll open the run app.


2. In the run app, enter:


3. This will add "Console" in your steam tabs.


For this example, I'll use Solenars Edge II: Aurora of The Seventh Dawn.

• 3.a. You'll need the "App ID" and "Achievement Name". To get them, open SteamDB[steamdb.info] then type the game in the search bar and choose the exact game you want from the selection.
  
  
  
• 3.b. In the game's steamdb page, click on "Achievements" on the left side.
  
  
  
• 3.c. The "API Name" is the achievement name. You can now see both the App ID and Achievement Name.
  

4. Return to the steam console and enter:

Some games are just persistent and the achievements will just come back after all that, what you can do is use this command:
BEWARE though, it will LOCK ALL the achievement in that game, BUT it will do the job ;)







If for some reason it's still failing, try to restart steam(exit steam & run it again) or restart the pc entirely then try again.
I've did it numerous times and a single restart seems to do the trick, I didn't encounter any problem after that.

If you find this helpful, please rate & favorite so other players can find this too. It means a lot to me, thank you! :)