A. Finding the Actions
1. Click on the + button, located at every intersection on your workflow.
A pop-up window appears.
2. Choose the Actions tab, on the pop-up that appears.
3. Click on the gray dot to navigate between pages of available actions.
4. Click on the Then increase / decrease custom field value option.
B. Setting up the Action
1. Select the custom field which you want to increase/decrease.
Notice how the available options on the drop-down list are any custom fields you've created of the Number Data type; the name of the list where each belongs indicated in brackets beside its name. If a subscriber triggers your automation, even though they are not subscribed on that particular mailing list to which the custom field belongs, then they will be added on that list automatically.
2. Select the increment/decrement type from the drop-down menu.
You have two options:
You can choose to increment / decrement a field by an absolute number (e.g. increase 2 by 5 to get 7) or by a percentage (e.g. increase 4 by 10% to get 4.4).
3. Fill-in the increment/decrement value.
The selected custom field will be increased or decreased by the value that you've set. For decreasing make sure that you use the minus sign "-".
4. Click on the Save button.
Your Action step will be ready and waiting inside your workflow.
If the available fields aren't enough you can always conjure up your own Custom Fields and then add them to your Action. Also, make sure that you explore the highly useful Conditional / Control steps which will help you design the perfect automation for your needs.