How update profile field with ubercart actions?

Hello.

I made event registration and i use UC Node Checkout and ubercart to make possible registration fee.

And i need to change value one of user profile field (profile_attendance value from 0 to 1) after customer make payment for special product.
I want to use Ubercart actions for this and possibility to execute custom php code if condition is true.

But i absolutelly new to php code for drupal.

Can you help please to write this part of code, please?

Thanks for you help.