A periodic EarlyWatch Alert already exists (see longtext)

You can only schedule one periodic EarlyWatch Alert using the Service
Data Control Center. (These EarlyWatch Alerts have a Z as the fourth
character of the session number.)
The following EarlyWatch Alert already exists: &V1&, task id &V2&

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

The Service Data Control Center only allows one periodic EarlyWatch
Alert to be created with a minimum period of seven days. This is to
prevent EarlyWatch Alert data from being sent to the SAP Service System
more than once a week. As the collected EarlyWatch Alert data is
aggregated by data collector jobs on a weekly basis, creating more than
one session per week would not provide any additional information for
the analysis report.
If you need to change the period of the periodic EarlyWatch Alert in
the Service Data Control Center, perform the following steps:
Delete the existing periodic EarlyWatch Alert session.
In the 'To do' view, select the session, then choose 'Delete'. If you
don't see the session, try extending the time frame of tasks displayed
by changing the settings at SDCCN->GoTo->Settings->User-Specific->
Display Tasks from.
Change the period of the EarlyWatch Alert.
Choose Goto -> Settings -> Task-specific.
A hierarchy of task-specific settings is displayed.
Choose Task-specific settings -> Session Data Collection -> Data
request -> Settings.
Change the period in field 'Repeat every'. (in 'Periodic sessions' ->
'Scheduling')
Create a new 'Request session data' Task for the EarlyWatch Alert.
Choose 'Create Task'-> 'Request session data'.
A dialog box is displayed.
Select 'Periodic' and 'EarlyWatch Alert'.

Error message extract from SAP system. Copyright SAP SE.