In many cases, it is possible. The usual case is just to type -
achievements = {score: 1} // I just made up the object structure. You should use the proper structure and values.
And press Enter.
If that does not work, you might be able to pause on a breakpoint in code that has the achievements variable in its scope/closure and then change it.
However, you should have some web development knowledge in order to do that (if you have it, you will probably easily find your way). This group is not really for non-web-developers.