Hi,
In your 'main' section after the Up and Down calls, the Units and Tens hold the value to be displayed.
You need to do a simple test on them to see if they are both Zero using the MOVF instruction, then the testing the Zero flag of the Status register BTFSS STATUS,Z
When they are both Zero you can turn ON - BSF PORTA,4 to activate your alarm.
However notice that the 7 seg drivers turn on PortA bits 0 and 1 but by changing all of PortA, you will have to change these to set just those two bits using BSF and BCF PORTA,0 and 1