Due to Minecraft's new default skins, anything above 1.19.3 for offline skins has to be a new layout, rather than the simple "textures > entity > Steve and Alex", which caused me some headache.
So, that means, if you are using above 1.19.3 you will not just have "alex" & "steve" pngs, however 7 more, these still follow the same princible however if you have already done this, before, just 7 more times.
Though, if you haven't done this before then, once you've setup the Recourse Pack, assuming you know how to put it in the correct folder, you are to extract the zip, open the folder and go all the way into the folder following assets until you've reached "players", once you have reached that folder open it up, you will see 2 folders, named "slim" and "wide", open one up it doesn't matter which and then you will see 9 names, don't worry too much on it, all you need to do is copy and paste your skin into the folder and change it's name for every skin currently in there, (please ensure you do not change the name in the slightest, it will not work.) after you have successfully done 1 folder, copy and paste it again, creating a copy of the folder you have changed, once done you can delete the other folder, renaming the copied folder the one you deleted, after all of this is done ensure that all of the folders and skins are lowercase, it won't work otherwise.
Now, you've got the easy side of the stick, as this is a lot more simple. Assuming you know how to setup a Resource Pack, you want to unzip it and go into the folder and go into assets, once you've entered the assets carry on going until you reach "entity" then open it, you will simply be shown 2 pngs, a "steve" and "alex", simply copy & paste your skin into the entity folder twice, deleting both "steve" and "alex" pngs when done, then change your pasted skins' name into the "alex" and "steve", then if done correctly, you will have it working.
Also, when setting up both 1.19.3+ and >1.19.3 folders, ensure everything that was spelt lowercase before is still lowercase. Otherwise, it wont work and you will have to redo this all again.
