At the moment, there is no option to reimburse expenses from Zoho Books. The option will be available soon.
As of now, in Zoho Expense, you can either mark your expenses as reimbursed or reimburse them online. When a reimbursement is recorded in Zoho Expense, transactions will be automatically posted in Zoho Books. You can view those transactions under the reports section of Zoho Books (Reports > Accountant > Account Transactions > Account name: Employee Reimbursement).