When you get the watch it will probably have last month's times on it.
Cancel last month's times by pressing "STOP?RESET". You will see a single zero and three rows, each with seven zeros.
When you are ready to start the race, press "START". As each handicap time comes up, start the runner. Don't press any buttons. The last runner will go off after, say 7 minutes 30 seconds. You've then got about 12m30s to wait for the first runner home.
As each runner comes home, press "START" (the other marshal gives the runner a tag). When the last runner is home, press "STOP?RESET". The number in brackets on the display (just below "SPLIT") shows the number of runners' times that you have recorded.
Press "RECALL". The top line of the display is the recorded time for each runner. Transfer these to the sheet and enter them against each runner's number. There's no need to try to turn the watch off.