CRM SDK - update entity's primary image to another field

Question

I am trying to update the existing entity's PrimaryImage attribute programmatically.

I have been trying to access the entity's attributes but couldn't find any regarding PrimaryImage.

Is it even possible to achieve that using CRM SDK request in C#? If yes, how can I achieve it?

I am trying with below approach:

var entityMetadata = RetrieveEntityMetadata(service);
entityMetadata.PrimaryImageAttribute = "ps_anotherPrimaryImage";

var updateEntityRequest = new UpdateEntityRequest();
updateEntityRequest.Entity = entityMetadata;