Two different questions:
1) Are you converting - applying for a Foreign-based certificate, or
2) Applying for a full FAA certificate, using existing experience and flight training?
Normally the 61.75 certificate is only issued at a FSDO within the US. Some delegate this to local DPEs (Florida especially), due to workload. I'm not sure if any DPE can complete the conversion.
For a regular issue, there are DPEs based in Europe. However, you would still need TSA clearance for training (for any level of initial FAA certificate, again for multi, and again for instrument). A sign off is also required for the Checkride from an FAA CFI.
Alternatively, you may find a reputable school that issues an M1 authorisation. This visa may come with the NIE, required to permit travel to the US from Europe for study, despite the Presidential proclamation. Student visa applications are still be processed by most embassies.
Good luck.