Cost Equivalent in US Dollar

I have a Corporate book in  Ringgit currency.  When Oracle converted this into US Dollar,  the  COST  dollar equivalent is not correct. How can I ensure that it picks up the correct rate  so  that it can compute the accurate cost USD equivalent of an asset. I would appreciate if you can tell  me the rate tables and/or set up.  Can I rerun or convert it again so it will pick the correct rate?  We already performed depreciation on those assets with incorrect cost  so we ended up entering the manual entries to take up the diffirence in depreciation expense.