How to replace name in a cell with another name according to a table?

Hello everyone. In an excel sheet, I have two columns where one of them corresponds to the names of communes and the one next to it corresponds to the districts of these communes. In another sheet, I try to ensure that in a column of a table, the name of the municipality is automatically replaced by the name of its district. How should I do it? What formula to use? Thank you in advance for your precious help.