When you remove a slice, its shares will not be taken outside the pie. It will set the slice target value to 0%, and the shares will be sold with priority during the next Rebalance or Withdrawal. The removed slice will be visible at the bottom of the pie's Holdings tab under the 'Removed from Pie' section.
To remove any slices from your pie, go to your pie's 'Holdings' screen and tap on the 'Edit Pie' button:
You will enter the 'Edit Pie' mode. Now tap on the (x) button next to the slices you want to remove.
After the slices are removed, the total target allocation of the pie will drop below 100%. In this case, you will need to increase the target values of one or more remaining slices in order to restore the total allocation to 100%.
You can also tap the blue circle showing the total percentage distribution. This way, the pie will suggest an auto-redistribution of the remaining percentages among the remaining slices.
Whenever you are ready with the changes, tap the 'Save' button.
Removing a slice is different to exporting investments. The latter action allows you to keep the desired shares outside the pie as Manual Investments. If you happen to remove a slice by accident, simply choose 'More Actions' at the bottom of the pie's Holdings tab, and tap the 'Export investments' option.