Hello !
There is nothing difficult at all, don't worry :3
Importing .json to gdevelop is super simple (Unzip→Open→Done!), however, on gdevelop mobile version, it doesn't allow you to import projects from your phone storage, only from Google Drive, and Google Drive doesn't support loading assets, so the solution is:
1- If you have a PC or laptop, install gdevelop desktop version.
2- Unzip the downloaded template (using WinRAR).
3- Open GDevelop on your PC.
4- Log in to your account.
5- Click on open project.
6- Select the .json template (that we unzipped in step 2).
7- Now Click on the 3 lines iocn in the top left corner to open the list.
8- Click on Save as.
9- Select Gdevelop Cloud.
10- After the saving is complete, you can close gdevelop from your PC.
11- Open GDevelop from your Mobile and log in to your account.
12- You will find the project saved in the list (My projects).
13- Select the project from the list to open it.
Note: you can also get any of my templates from GDevelop store directly from your mobile, doing that will save the project directly into your account, so you don't have to do any of the steps above if you got it from the store.