Hi @Abid_81,
Yes, currently there is no Excel trigger can be used. If you want to trigger a flow depends on if the remaining due dates reach to 30 days, you may try to use the trigger “Recurrence”.
Then get rows from the Excel table. After the get rows action, use a Condition to check whether the due dates reach to 30 days.
The flow could be configured likes below.
The function in the Condition is:
@equals(formatDateTime(items('Apply_to_each')?['When'],'yyyy-MM-dd'),formatDateTime(adddays(utcnow(),30),'yyyy-MM-dd'))
Then when the date in the Excel table is equal to today plus 30 days, a notification would be sent.

More details about formatDateTime and adddays function, please check it at here:
https://docs.microsoft.com/en-us/azure/logic-apps/logic-apps-workflow-definition-language
This doc on the trigger Recurrence could also be your reference:
https://docs.microsoft.com/en-us/flow/run-scheduled-tasks
Please feel free reply if you need more help.
Best regards,
Mabel Mao