im trying to start running after beating a geno run but when i delete the save data from user-(name)-appdata-local-undertale it reappears after launching the game with the same 'wind void' the genocide ending has.

ive wiped save data like this before, is there something specific im missing? the only thing in there is system_information_962 and it reappears even after fulling deleting it in recycling bin.

thanks in advance

You have to have Undertale disconnected from Steam. To do that, delete steam_api.dll in the folder which your Undertale exe file is located (usually C:\Program Files (x86)\Steam\steamapps\common\Undertale)