Since the address part of the instruction is 10 bits, I assume instruction length is 16 bits = 2 bytes.
So, PC value during execution of branch instruction = 620 + 2 = 622 (PC always contains the next instruction address)
Now, branch is PC relative and the address to jump is 530, the operand will be 530 - 622 = -92 = (10100100)2 (2's complement representation. )