What game and are u using ftpiiu or sdcafiine or are u on 3 DS

if the mac book has a sd slot go to a trusted modding site download and get the title id example: 0000-0000 make a file in the sd caffine folder name it the title id (remove the hyphen aka -) then put the mod in there if the macbook has no sd slot use ftpiiu and usea ftp client

you can also use an sd adapter with a usbc outlet too, also get ur mods from a trusted website like gamebanana or sumthing

personally, i use gamebanna for my mods it scan files for virus