From your Shopify admin, go to Settings (bottom left sidebar)
Click on Locations

You can add new locations if you have multiple stores or warehouses
After that, select the location that you want to enable store pickup for

Make sure to add:
Address
Phone number
This step is required for the pickup option to work properly
Inside the selected location, ensure Fulfillment is enabled

Go to Pickup in store
Enable the option Location status
If you would like our team to check your setup, please contact us on Live chat.