Sending a hidden field in a content type when creating or updating

Hi, I need the send the timezone offset when the user is creating/updating a content. I already added the field “offset” to the content type, but I want it to be hidden and set programmatically to send the actual timezone offset.
Do you which file I need to edit to achieve this goal? I tried forcing the value in /extensions/content-manager/admin/src/components/Inputs/index.js but even though it displays the value in the text input, it doesn’t send the value when doing the post. I guess I need to actually change the form state to add the value before posting it. Any ideas on how to do it?