Please execute poxrespo.sql in ebsdev instance which is located at $PO_TOP/sql?

For instruction or for more assistance you can below metalink id.
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How To Reset a Purchase Order or Requisition From In Process or Pre-Approved 
To Incomplete/Requires Reapproval For Isolated Cases [ID 390023.1]

1)For instruction check metalink id  [ID 390023.1]
2)Go to cd $PO_TOP/sql and run poxrespo.sql in apps schema.

cd $PO_TOP/sql


SQL> select name,user from v$database;

NAME USER
--------- ------------------------------
ebsdev APPS

SQL>

SQL> @poxrespo.sql
DOC> | Copyright (c) 1997 Oracle Corporation Redwood Shores, California, USA|
DOC> | All rights reserved. |
DOC> +=======================================================================*/
DOC>
DOC> This script will:
DOC>* reset the document to incomplete/requires reapproval status.
DOC>* delete/update action history as desired (refere note 390023.1 for more details).
DOC>* abort all the related workflows
DOC>
DOC>If using encumbrance it will also:
DOC>* correct po encumbrance values if corrupted
DOC>* Suggest gl manual postings to have the gl data in synch.
DOC>*/


Please enter the PO number to reset : 435750237
Please enter the organization id to which the PO belongs (Default NULL) : 1155
Do you want to delete the action history since the last approval ? (Y/N) N

table already exists, hence not creating again

PL/SQL procedure successfully completed.

SQL>

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