How is reimbursement done when someone other than the business pays the bill?
owner will often pay for things from own money.
If you are a sole trader then there is no reimbursement. You are the business so there is no concept of paying you back. It does get deducted off your company tax bill, but you don't get the money back.
If you are a limited company then you can get reimbursed - you do that via Payroll. That is the only way you can legally get reimbursed.