The EPCS4SI8N is a SPI based FLASH memory to store the FPGA configuration bit stream. It is connected to the EP3C10F256C8N FPGA. On power up the EP3C10F256C8N reads data from the EPCS4SI8N to configure it self.
It depends on what failed on your board what needs to be replaced. If the EPCS4SI8N lost a couple of bits, but is still functional otherwise, it might be possible to reprogram it, but you need a working board to read the original data from that EPCS4SI8N.
To get a better understanding read the datasheet of both the IC's