seat selection on DL

I have a SFO-JFK-LHR ticket on DL and VS.
I am familiar with seat assignment for VS but cannot figure how to select a seat or do OLCI for DL (tkt issued by VS) ?

I have a SFO-JFK-LHR ticket on DL and VS.
I am familiar with seat assignment for VS but cannot figure how to select a seat or do OLCI for DL (tkt issued by VS) ?

Assuming it's a service they offer, you'll need to get the DL booking reference from VS. Once you have that you should be able to plug directly into the DL systems.