Macro to replace value on sheet with a value from another sheet

[rpadminserver]

Hello All..
Quick history:
We have assets that are known by what we call "external" name. This external name is an unique identifier. But... When our oracle database was created, this external name was not used has the key field, another "internal" name was used.
Example
External name = 987654 Internal name is 1111
External name = 876543 Internal name is 2222
External name = 765432 Internal name is 3333
Problem:
I'm creating a speadsheet what will be saved as a CSV file and used for uploading to the oracle tables. This spread sheet will have 2 tabs "Upload" and "Assetmatch"
Upload is where our work is done and where the user will have to enter the External name. the Assetmatch tab will have the external name/internal name relation.
Before saving as the CSV file (and the upload can be done) the External Name needs to be replace with the internal name on the upload tab. So.... I'm looking for a macro what will do that.
On the UPLOAD tab, the external name will always be column A. On the Assetmatch tab, the external name will column A and the internal name will be column B.

Thanks all.