Mine sounded acceptable after I did some editing.

In Editable Notation Mode, right-click on the note, select Edit Note and it brings up a dialog box where you can adjust things like volume, channel, pitch, duration and time. Time means starting time for the note, expressed in measure number, beat number, and tick number.

Set the start time of the first note in the triplet to bar x, beat 2, tick 0.
The second note would be x, 2, 80.
The third note would be x, 3, 40.

Depending on how you enter the notes and whether or not you have non-zero entries in Edit, Slide Tracks, your tick numbers may not be exactly 0,80 and 40. They might instead look like 7, 87, 47. But you see the pattern, because 120 = a full quarter note (unless you've changed the default). So 0 is the beginning, 80 is 2/3 of the way through that beat, and 40 is 1/3 the way through the next beat. Triplets.

BIAB 2024 Win Audiophile. Software: Studio One 6.5 Pro, Swam horns, Acoustica-7, Notion 6; Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus Studio 192, Presonus Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors