i need some help to modify World Conqueror 3

You don't need root the mod

Ok, good. Install Hex Editor, Total Commander and Apk Editor if you haven't installed it already.

Only three things are not possible on mobile or just incompatible, like if you want to have control over aliens you will have to do it on a computer and install a hex editor I think. I actually don't know how you can make yourself control the aliens and make a new level and I don't know if it it's possible to make a new level or not. Making a country is complicated and hard, I don't know how to make a country myself but it is possible.

If you want to modify generals, first you have to use the Total Commander app then do the following steps:
Step 1: Open Total Commander
Step 2: Find World Conqueror 3, (if you download World Conqueror 3 it will usually be in the map called ''Download'')
Step 3: Click on it, then click open as zip.
Step 4: Click the map assets
Step 5: Click the map called json
Step 6: Find the CommanderSettings.json and click on it.
Step 7: You are now in the commanders file, you can edit the stats and modify the commanders in the file.

As for modifying and editing music, you also go to Assets, then click audio map on the top of the list.

If you want to unlock all the conquest years, follow the following steps:
Step 1: Open Total Commander
Step 2: Find World Conqueror 3, (if you download World Conqueror 3 it will usually be in the map called ''Download'')
Step 3: Click on it, then click open as zip.
Step 4: Click the map assets
Step 5: Click the map called json
Step 6: Find the ConquerSettings.json and click on it.
Step 7: Click and hold your finger on the conquersettings.json file.
Step 8: Click Extract+Edit
Step 9: Change all "unlocktime" to 1939.1.1

You can modify the resources in HQ settings but I don't know about the medals.

Edit: 

Changing allies might be hard for the first time but I will try my best to explain how:
Step 1: Open Total Commander

Step 2: Find World Conqueror 3, (if you download World Conqueror 3 it will usually be in the map called ''Download'')

Step 3: Click on it, then click open as zip.

Step 4: Scroll down until you see one the conquests files. There are 5 conquest files: conquest1001.btl (1939), conquest1002.btl (1943), conquest1003.btl (1950) , conquest1004.btl, (1960) conquest1005.btl (1975 aliens)
Step 5: Click and hold on the conquest that you want to change
Step 6: Click Extract + edit, then you will see "Edit with (app)'' Click on Hex Editor 
Step 7: You should see some numbers now, don't worry. Zoom out until you see 4 columns of numbers.
Step 8: For example, you want to edit the United Kingdom to be Axis instead of Allies. Find the country code of UK. (fa fa 96 00) if you can't find it, click on the search icon above and type in the country code, you will have to type in fafa9600. If you type it with spaces it won't see it so don't type it with spaces.
Step 9: Search for the 04 from left to right or above (applies to every country). If you followed all the steps you will see that 04 is all the way to the left. Don't look at the white numbers and .
Step 10: If you found 04, go search for 02. It will be above of fa fa 96 00 in this case. In other cases it will be above or left from the countrycode.
Step 11: You should have found 02 now, click on it and change it to 01 in order to change the UK to be on the side of the axis.

Sides:
01 = Axis
02 = Allies
03 = WTO (Warsaw Pact)
04 = NATO
05 = Union
06 = Aliens

Things might be unclear, just ask and tell me if they are a little bit unclear and if you don't understand.