when i started used the nsmb u asm patch. in the editor when i use custom tilesets all is ok
but when i start the game. the custom tilesets dont work!. it shows the normal tileset.
can someone help me?

that's because of meromero's dedicated tileset per area hack. basically means all of the tilesets you can access in the tileset tab don't matter. the tileset files the game uses are in a new folder. you need to edit those files instead.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

how i change these?

that's unfortunately a bit of a pain. you make a custom tileset using any slot in the tileset tab, you then look up which files the slot you used uses, you extract those files and then you replace the files the asm hack uses with the files you extracted.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

Idk where are all these files. I used an usa PSYDS rom and idk where are the asm files. ill try to search mroe about that thing

edit:
i already found the ASM files and. idk what to do now