To setup a 2nd lever approver, please follow the below steps:
Navigate to post setup Admin Menu or Configuration depending on how you have your system configured.
Click on the post you want to amend and drop-down Approval on the left and click on Approvers.
You can set a second approval level for any of the options.
Click on the one you wish and then click on Add Approval Level.
It defaults to Auto Approve at second level, but you can change it to use an Approval Group or Select Approver.
Once you have selected who you want to be the second line of approval click Save.