How about entering 10,000 miles total for each business?

Or, put all on one business. Subtract the expenses calculated for the other business and input that amount as expense on the other business. EX: Total auto expense 8,200 computed for Sch C 1. Enter -3,000. Net 5,200.

Sch C 2 enter 3,000 auto expense.

Or, why are you using two Sch Cs?