1. Open Group Policy Editor (gpedit.msc).
2. Choose Computer Configuration > Administrative Templates, right click on it and choose Add/Remove Templates…
If you were applying settings to users, you would choose User Configuration.
3. Browse to the location of the required .ADM or .ADMX file and click Open.
4. In the Add/Remove Templates window notice that the new added file is listed, then click Close.
5. Now the template is listed in the Classic Administrative Templates.