I'm not too sure what you mean by "reverse it" - can you clarify what you are trying to achieve?
However, you can convert a string representation of a datetime value with the timezone ("2021-04-07T11:40:29-0400") to a datetime type using the Modify Fields node.
The Format specification for parsing the string is yyyy-MM-dd'T'HH:mm:ssZ

Once you have the value as a datetime type you can then extract the elements of the datetime value (using the Calculate Fields node in this case):

In the above, the elements were extracted as strings but you could change the Type choice in the above to "int" to convert the Year through Second elements to integer values.
See the attached example data flow (requires Analyze 3.6.x).
Attached files
Convert_Timestamp - 8 Apr 2021.lna