Blender 2.8 - Object/Mesh Dimensions perplexity - Help please Beginner here &amp; also the first time searching for help here

I'm modeling a Sword for a Melee Slasher Game &amp;
without an offical SDK(soon), i'm only able to exchange existing Models.

This means i've to keep/use the exact Scales/Dimensions of an existing Sword in the Game, because of the same Hitboxes they've to use etc.

So i converted the UE4 File into .fbx and imported it into Blender
Scale/Dimensions are this:


Then i build my own Sword in the same Project, to adjust and keep the Dimensions to the Original Sword i'm trying to replace later.

As a Beginner, i once made the mistake and couldnt merge by distance as expected and made my Sword something like 20x times bigger in all directions to merge by distance to get the result i wanted.

Now i cant rescale my Sword-Mesh properly &amp; i'm searching for ages for a solution on the web.
This is how it looks, when i'm just typing in the Dimensions of the Original:

(Unmarked Sword-Mesh=Original / Marked Sword-Mesh=My Model)

(The Dimensions dont fit to my 20x statement anymore, because i already tried many rescalings)

And this is, how it approximately should look like:


I dont want to rebuild the whole Sword, even though it could help me to get a better workflow and so on.., but for now i want a solution to this problem,
because i could run into this later again.
Could somebody give me a Step-by-Step Guide, how to fix that?
Your scale values are locked 



Click locks to unlock. 
Then scale your model to match reference sword. Scale values may not be 1. You can apply scale (Ctrl + a) to make scale values 1. 

Or else switch to edit mode, select all vertex and perform the scaling. Doing so won't alter your model scale values