[for macOS]
If you want to delete a project go to:
~/Library/Application Support/com.SebastianLague.DigitalLogicSim/SaveData
Here, delete the folder that has the name of the project you want to delete.
If you want to delete a chip from a project but not the project go inside the folder that has the name of the project and delete the file for the chip (e.g. You want to delete the NAND chip you've created: go to the location and delete NAND.txt)
NOTE: The data could also be located at:
/Library/Application Support/com.SebastianLague.DigitalLogicSim/SaveData