Hello,
Click in the measure with the quick entry tool. Hit “Option 3” then hit 3 three times or 4 three times or what ever the note value you want, 3 times. Then go back into the measure and delete the middle note, then go to the first note and make it a quarter note (or what ever figure you want)v thus completing the triplet.
I’m sure you probably already know this part so far!
Then highlight that figure and drag it to the second beat. Highlight beats one and two and drag those to beats 3 & 4 (assuming you're in 4).
Copy that measure, rinse, repeat.
Thomas