If you find where the Undertale save files are located, you can delete them and start fresh. According to this Steam forum post, the save files are in appdata\local\UNDERTALE on Windows, ~/Library/Application Support/com. tobyfox. undertale/ on Mac. undertale naming yourself chara? undertale what happens if you name yourself sans.

How do I delete my Undertale save file?

If you find where the Undertale save files are located, you can delete them and start fresh. According to this Steam forum post, the save files are in appdata\local\UNDERTALE on Windows, ~/Library/Application Support/com. tobyfox. undertale/ on Mac.

How do I reset my Undertale data?

I don’t have it on Switch but the truest reset should be: System settings > Data management > Manage save data > Delete save data > Undertale.