Ok. I solved it myself.

I created a new automation rule in Settings > Automation Rules. 

Trigger: State is set to: "Sales Order"

Action: "Execute Code"

And used the below code

--

weekdays = ['Monday','Tuesday','Wednesday','Thursday','Friday','Saturday','Sunday']

# Get today's date (in server time)

today = datetime.date.today()

today_name = today.strftime('%A')

target_day = record.x_studio_delivery_day

if target_day in weekdays:

    days_until = (weekdays.index(target_day) - weekdays.index(today_name) + 7) % 7

    days_until = days_until or 7

    new_date = today + datetime.timedelta(days=days_until)

    # Combine with 8:00 AM time

    new_datetime = datetime.datetime.combine(new_date, datetime.time(9, 0))

else:

    new_date = False

record.write({'commitment_date': new_datetime})