PUT Image ID to Entry

Im trying to update a entry file using an existing image ID but when i try something like:
await strapi.services.transcript.update(
id,
{ file: existingFile.id }
);
when i get the entry i get “file”: {} but if i get the image it have something like:
“related”: [
{
“__contentType”: “Transcript”,
“id”: 1444,

},