I think John may want three quarter notes played over two beats.
The default resolution depends on the style. Since you say your song has even 8ths, it is what BIAB calls an even style as opposed to a swing style. John, I assume your selected style appears in the Style Picker as Even8 or maybe Even16. For either, the answer is the same. If my assumption is wrong, please write back.
What I do, which may not be the most efficient way but it works, is the following:
In Editable Notation Mode, there are four vertical dotted lines per beat, for a total of 16 vertical dotted lines per measure. I enter my first two quarter notes on the first and fifth vertical line. Then for the triplet, I enter a note on the 9th, 12th, and 15th line.
It looks bad, but wait, we're not done.
Then I right-click on what will be the middle note of the triplet, line 12, and change the timing from x(measure), 3 (beat) 97 or some number like that, to 80 for the last number, which they call the tick. Why? There are by default 120 ticks in a beat, so 80 is 2/3 of that. Continuing, I right-click on the final triplet note and change the tick number from 67 or so to 40. 40 is 1/3 through the final beat. This makes it a quarter note triplet.
This will now SOUND correct.
If it's important that it LOOK correct, you can click on the Opt. icon, 5th row down, far left, and select Triplet Resolution. It will be Unchecked, since you had selected a style that is NOT Swing. Then in Leadsheet Mode, you will see actual quarter note triplets.
If all that sounds tedious, what I do when I have this figure occurring many times in a song is copy that measure to the other locations, and change the pitches if needed. Not so bad.
At the risk of confusing you further, there is an FAQ about this with more information, and they take a different approach.
https://www.pgmusic.com/techfaq69.htm#25