Web API: Creating and updating a single rest resource through multi-step form?

We have multi step form where user fills his personnal details.

1. In step1, we ask name, email, and mobile.
2. In step2, we ask educational qualifications.
3. In step3, we work experience details.

I am planning to create single REST resource for this i.e. /api/user/

I want to update the information sent from client to server in the database at each step. I don't want final step i.e. step3 to send all the resource data in one go.

The problem is that once we send data at step1, the API would give validation errors for required fields that are yet to be filled by user in step 2 and step3.

What could be solution for this partial update problem? One is using PATCH request, do we have any other solution?