An insert into select query will do what you want. I'm making no comment on whether or not your db design is correct, or at least the best way to go about it, but this SQL query will do what you've asked in the OP:
I've made some assumptions about datatypes and form/combo box names here but hopefully this will give you the idea:
Code:
INSERT INTO T_Record ( Task, MSL_Name, Date_Assign, Complete, Date_Deadline )
SELECT T_Tasks.Task, [Forms]![MyForm]![cmbEmployees] AS EmployeeID, Now() AS AssignDate, False AS IsComplete, Date()+30 AS DueDate
FROM T_Tasks
WHERE T_Tasks.Unit_ID=[Forms]![MyForm]![cmbUnits];
This will select all the tasks that belong to a unit and add a record in T_Record for each task, assigned to the specified employee.
Save this as a query then just have a button on your form call the query.
Take a look at this study material: https://www.w3schools.com/sql/sql_in...nto_select.asp