Simplest way I can think of is:
Create a global variable counter
system every 0.5 seconds
system compare two values counter < score
- system add 1 to counter
- currentscore set text to counter
Perhaps add something like:
maxcounttime = 180 (3 sec x 60 ticks per sec)
scorecounter = int(score / maxcounttime)
sub int(text.text) < score
action: set text.text = int(text.text) + scorecounter
This theoretically would give a 3 second counting function to count from 0 to your score.
I suggest this because, if you would have a very high score, the counting could take long. this function dynamically reduces counting to 3 seconds (180 ticks).