I assume by your limited info that you play on PC but don't use any mods at all? Otherwise you'd know what Sider is.
suggest you go check the sider thread:
https://evoweb.uk/threads/sider-7.84002/ and familiarise yourself on what the tool is and how it works.
In summary, sider lets you 'side load' user created mods into the full game, so you can add in new turfs, balls, scoreboards, adboards, logos etc.
If all you want to do though is basic editing such as emblem, kit etc, then you can do that via the in-game editor, unless you want to edit a licensed team, then it is locked, as you mention.
To get around this you could either use the teams de-licensing tool (google it) or install sider and kitserver, then produce the kits in ftex format and load via kitserver