You should file two separate schedule Cs for your independent contractor jobs, keeping all expenses and income separate.
Let's do Uber first. You report your gross income, and you can deduct personal vehicle expenses using the standard mileage method or the exact expense method, as described in chapter 4 of publication 463.
https://www.irs.gov/pub/irs-pdf/p463.pdf
The standard mileage method requires less detailed records and results in a higher reimbursement for most workers unless your vehicle is brand new or very expensive.
As an independent contractor for customer #1 (you don't "have a job" if you are an independent contractor, you are a business providing a service for your clients), your client can either reimburse you based on an accountable plan (where you prove exact miles with records), or a non-accountable plan.
If an accountable plan, you do not report the mileage reimbursement as part of your gross income unless it is more than the IRS standard rate. (If they pay more than the IRS standard rate, the difference must be included as part of your gross taxable income even if it is not on your 1099-NEC.) You also do not list your miles as a deductible expense. It's not taxable income and not a deduction.
If they use a non-accountable plan (you are not required to prove mileage with records), then the amount of the reimbursement is included in your gross business income on schedule C, even if it is not included in your 1099-NEC. You then can list your miles at the standard mileage rate, or your actual vehicle expenses, using the methods mentioned above. You can deduct your mileage against the income if you have records to prove it.
You must separately track the mileage for your two different jobs and report them separately on two different schedule C businesses along with any other separate income and expenses.
