Enough space on Minecraft switch

Hello, 

I am a french mother so I may not well explain the problem. My son plays Minecraft on his switch console. Since december the 25th, he has a message when he opens his game. Not enought space... Minecraft had blocked the game until you delete some maps. The switch console has only 20% of occupied space. How can he plays to his game without re initialized his console . Thanks a lot. Have a nice day