Whichever method you choose, it should be the same for both businesses.
If you use the standard mileage allowance, it should be easy to divide the expenses between the two businesses, assuming you kept separate mileage records for each.
If you use actual expenses, you will need to divide the expenses proportionately according to the mileage for each business.
See the answer below for more information.
https://ttlc.intuit.com/replies/5135131