Good day, I was wondering if you could help me with something that I tried to do but failed misserably.

We have accounts on our system that did not have any Account numbers assigned to them. After our company has grown we now have use for these company Account numbers. We tried exporting a few test companies into excel and then manually adding the account numbers to the field and then importing them back into the system. but instead of adding onto the previously existing accounts, by just adding the missing account numbers that we allocated to them. It instead created new copies of the test companies. I was hoping to ask if it were possible for us to be able to add these assigned account numbers to pre-existing acccounts or do we just have to go and do it manually for hundreds of companies