Hello @Jerome MAISETTI
You can use the below script in Before Update BR:
Condition: State is on Hold AND On hold reason changes to Pending Customer
Before update BR Script:
var nowGDT = new GlideDateTime();
nowGDT.addDays(3);
var nowDateNumericValue = nowGDT.getNumericValue();
current.<your_date_time_field_name>.setDateNumericValue(nowDateNumericValue);
