Hi Fernando Luna,
You can display the log of posted valuation documents using program FAGL_PROT. If I am not wrong, there is no direct transaction for this program in Easy Access. Otherwise you can see the valuation documents posted with specific document type that you might have used for your valuation area.
Once you identify the valuation documents that were posted in previous valuation run, then you need to manually post reversal documents for them. You can use normal FI journal posting transactions like FB50, F-02, etc and the posting keys to be used will be the reverse of the original valuation postings thereby nullifying the effect in books. Yes you may need to re-open previous periods in FI and CO when there is long overdue of these postings.
No, there is no other functionality in FAGL_FC_VAL or FAGL_FCV to post missing reversal postings later on after the successful execution of initial valuation postings.
Regards,
Sridhar