Please follow the below steps-
1. Log into Opencart Admin panel of your store
2. Go to Extensions > Shipping from the left column.
3. On this page, you will find already enabled and disabled shipping methods.
4. To add a new, please click on + icon at the top right corner and input the information and delivery cost.
5. Select the desired delivery zone and after saving the module, it will be visible on checkout page delivery options.
Hope, it will help.