Please refer following interrupt sources table from "PSoC 41XX_BLE/42XX_BLE Family PSoC 4 BLE Architecture TRM, Document No. 001-92738"
The WDT interrupts requests are assigned to the interrupt source IRQ8. You can configure the interrupt number. For example,
(void)CyIntSetVector(8u, &CySysWdtIsr); CyIntEnable(8u);
These codes are contained in the auto generated file cyfitter_cfg.c
You can use a function "void CyIntSetPriority(uint8 number, uint8 priority)" to set the priority.