[RedSector]

Still under warranty, then take it to them.
If not, you need to clean all the oil off with a suitable degreaser and then watch for the leak, could be a valve cover or an injector(s) seats, leak off (as mentioned), would be my thoughts initially. Assuming no DTC's or other issues happening.

Helps if you provide the Engine Designation Code from positions 6,7,8 of the VIN.

 

[RedSector]

Likely be identical to a (at least for engine related components, possibly more)
PEUGEOT 308 (T9) 1.6 HDi 120 DV6FC (BHZ) 2014 - Onward
might be useful to know this is likely.

These are both covered in Peugeot servicebox online for OEM parts and information. (can be paywalled access, never sure how it works, I don't use it)