If you want to delete data records in Magpi+, simply:

1 - tap on the form that contains the records you want to delete.  That brings you to the record list for that form.

2 - swipe from right to left on the record you want to delete. That will reveal a red button.

3 - tap the red button and you'll see the delete dialog

4 - click OK and the record will be permanently delete.

Note that deleting records from the Magpi+ mobile app does not delete them from the Magpi website, if they've already been uploaded.