[HELP] Importing custom blips

Hello, a lovely community of FiveM,

I’m a bit stuck… No. I’m not here to ask “pls how do I add blips thanks mod help me thx”. I’ve seen some servers with custom blips (blips that don’t have ID’s on docs), almost like replacing that blip with another. Does anyone know how to do it? It’s something that’s really got me thinking…

Thanks!