Follow the below steps to create an Approval Process:
1. Go to SetUp → Enter Approval Process in Quick Find box → Select Approval Process.
2. For Manage Approval Process For, Select Opportunity.
3. Click Create New Approval Process → Select Use Jump Start Wizard.
4. Configure the approval process.
5. Save the approval process.
6. Click View Approval Process Detail Page.
7. Under Final Approval Actions, click Add New | Field Update, and configure it with your values.
8. Click Save
9. Under Final Rejection Actions, click Add New | Field Update, and configure it with your values.
10. Click Save