Yes this is possible.
Once a pattern has been set, "--" will be displayed in the schedule field even if the pattern is subsequently removed.
This is because the attendance data on the day when the edit operation is performed once is provisionally compensated with "--" and displayed because the schedule must be registered on the system .
How to delete
Follow the procedure below to delete. If you perform the following operations, the time stamp data/schedule data will be lost.
Daily data > [Display]> [Time card] of target person> [Edit work] on target day> "Completely delete work" at the bottom of the screen
Daily data ＞ Specify the target date and click [Display] ＞ [Edit] of the target person ＞ "Completely delete work" at the bottom of the screen