Under Settings > Advanced > Approvals, you can turn on the Require all approvals when manual appointing on or off in the company account by checking or unchecking the box:
This option applies to cases where one or more approvers have been manually appointed for an expense (appointed on the expense overview vs. through a workflow rule):
If the setting is unchecked...
...then an expense can be approved by just one coworker, even if several coworkers have been manually appointed to approve the expense.
For example, if three employees have been manually appointed to approve an expense, approval will be complete as soon as the first of the three employees approves it.
If this setting is checked...
...then the expense approval will only be complete after all the employees who have been manually appointed have approved the expense.
For example, if three employees have been manually appointed to approve an expense, approval will be complete only after all three have approved it.