I haven’t had any success in the past with ‘logged in user’ functionality, so I’m not sure doing this automatically will be possible.
I have done this for clients before. They didn’t share ‘ownership change’ capability, so we did it differently for each client (due to other config inside their system):
For one, we had a custom field with a dropdown list of all ‘users’ in the system. We ran a decision diamond after the Internal Form saying “if X field = Joe Smith” they would go into sequence 1. There, we would ‘assign owner’ to Joe Smith. Repeat for all options.
For the other, we just had a Radio button with all potential ‘users’ listed and did the same process based on the option chosen in the radio button field.