You can change the icons of the One Step Checkout steps in these files below

[icons Billing-address] app\code\Mageplaza\Osc\view\frontend\web\template\container\address\billing-address.html

[icons Shipping-address] app\code\Mageplaza\Osc\view\frontend\web\template\container\address\shipping-address.html

[icons Payment] app\code\Mageplaza\Osc\view\frontend\web\template\container\payment.html

Updated on: 01 / 26 / 2021