I loaded a landscape from the marketplace and that made the player that I control not appear unless I play. Now I can’t change the mesh of the character.
You can find your character in the content browser or in the Ctrl+P menu
The player that appears for levels with no player placed in the is the default player from your game mode.
So, as Tuerer says, you just need to edit your default character. If you type CTRL-P and type thirdpersoncharacter, you’ll see all the places in your project where this player type is defined.
Just take the one with is not in one of your asset packages ( they often contain characters ).