Yep yep and yep sure sounds to me like you have shut down the heater and turned off the pilot light.
Firstly I do not know which of the models you have there but I am going to assume that your unit follows the same system as most of the others so here we go …
To restart the heater you have to firstly press in the plain button to as you say “reset” the heater, then press in and hold in the single flame button whislt at the same time repeatidly pushing in and out the “striker” button which lights the pilot light, once the pilot light is going continue to hold in the plain button for 20 seconds or so then slowly allow the button to work it’s way back out, then press in the “3 flames” button and the heater should now work when the tap is turned on.
If not you will have to call in a serviceperson to get it going for you.
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians