1. You may want to delete existing data first to avoid mixing up existing data and imported data by the following.
From File -> Open data folder -> history -> MetaTrader4 server name you are using > remove .hst extension from the name of the currency pair you want to import historical data.
2. Select "Tools"->"History Center"
3. Double click on the relevant currency pair and the chart timeframe, wait till the database icon becomes active and the data is shown in the window as below
4. Click "Import" -> OK
5. Restart MT4 to reflect the change
please note that the downloaded data is provided by the MetaQuotes Company and may differ from our company’s data.