I think your request is too broad. ITUB, for example is an Italian company and has ADRs traded in several stock exchanges. Hence, if you do search in Eikon, you find multiple tickers for it.
And I failed to find critea, which could yield single return value for each tickers you supplied.
I used request: =RSearch("Equity", "TickerSymbol:" & B3 & "*") where you place your ticker into B3 cell.
For GIRO there are:
For BITA I had:
And there were ever more tickers for ITUB.
When I added search criteria, number of results decreased.
I have no Bloomberg, but when I used http://bsym.bloomberg.com/sym/ I had similar results:
Market Sector: Equity
Security Type: ADR, Common Stock
And there were 14 BBGIDs.
Hence, I think there's no direct way to do it.