You will need to remove the undertray
Undo the undertray fixings
Carefully remove the undertray
Don't forget to have a suitably sized receiving container in place
With an oil catchment container in position, use a 21mm spanner or socket to carefully remove the sump plug and fully drain the oil.
When the sump has emptied, wipe clean the sump plug area with a paper towel and refit the sump plug and washer. Replace the undertray