Second approval from RFQ to PO (based on amount) in odoo

Step 1 :  Go to Settings > Purchase > tick the field " Force two levels of approvals " and also you can set the limit amount in " limit to require a second approval ".

so when purchase order exceed this limit of amount. then system will ask for second approval from manager.

Step 2 : you can see in below screen shot that system showing second approved button for approval.