Transaction FPG1 - Transfer to FI

Good day

I need assistance please.

I have done a FICA transfer with transaction FPG1. Errors occured on the transfer which prevented it from posting to FI. Before I could  do the transfer the reconciliation key has to be closed.

Unfortunately I cannot fix the error on the FI side as it was a valuation rule that was created in GL.

I need to correct a transaction in the reconciliation key to enable the posting to FI.

How can I correct an entry if the reconciliation key is closed already or how can I reverse a closed reconciliation key?

Is there a way that I can do a simulation posting to FI so that errors can be determined and corrected before I close the reconciliation key?

Thank you for your assistance, much appreciated.

Maatjie Prinsloo.