You can import historical data from a 3rd party in a chart by the following;
1. In MT5, select "View"->"Symbols".
2. In 'Bars' tab, click 'Create Custom Symbol' and select the pair you want import data in 'Copy from' drop down menu, then double click on 'Symbol' to change name of the pairs, click ok. *You need to specify different name
3. Click 'OK' then change the pair name to the one you chose. Click 'Import Bars' and specify a file path you want to import from 'Browse', select import details then click 'OK'.
4. Once data is shown in Data window, click 'OK' to complete.