Depends on how deep the target indication is.
As mentioned above for 1 to 3 inch deep targets use a smoothed out tip screwdriver.
I've dug a lot of plugs over the years, i know what works and what don't.
For medium to deep targets i'm not a fan of the smaller the plug the better.
For these i slice down a rough deep semi-circle, deeper than than probably necessary.
Here's my take right or wrong on plugs:
-A deep plug will typically keep most of the deeper root structure intact, especially important in hot dry weather.
-In parks, a deep plug will resist being pulled out and flung a few feet away by the vacuum of the park mower. Seen flung dried up plugs more times than i care to remember. A real eye sore to me and i'm sure the park caretaker too.
-Also do not leave a plug higher than the grade around it. It will likely dry up and worse be spotted a mile away.
The replaced plug should be approx. an 1/8 to a 1/4 inch or so below the surrounding grade. This will ensure the next rain will puddle over the plug and help rejuvenate it. Sometimes highly compacted soil when dug up and loosened will be too much to put back in the hole. My solution in that case is to grind that excess soil up with the hands and fling it into the air. I guarantee it will not be noticed if done right. But a dried up plug a couple inches higher than its surroundings will be noticed.
I seen guys stomping, pounding and jumping on a plug to try and get it even with its surroundings. Ain't gonna work, all that now hyper compacted soil can't be condusive to keep the plug alive.
-Make sure the periphery of the plug is well sealed with soil. I've seen dried up plugs that looked like an earthquake happened around it. Without soil around the plug's periphery, the air will get in and dry up the exposed roots. Seen lots of those, plug is dried up around its edges but greener towards the middle. I always save a handful or two of soil for this purpose.