How Can I tab this guitar bend out?

Since version 4.2, this has been "by design": https://musescore.org/en/handbook/4/guitar-bends#general-points

You wrote:
Whenever I add the bend, it replaces the 2nd note in the triplet & holds the bend for 1st and 2nd note of the triplet????

According to the handbook:
"In general, bends in MuseScore connect two notes together: a ‘starting note’ and an ‘arrival note’."

From your images it looks like you want the triplet to sound as 3 notes - a full bend on the D, followed by an E, followed by an A. You do not want the 1st and 2nd note of the triplet to be combined into a bend.

One way is to have the ‘starting note’ and the ‘arrival note’ played during the first third of the triplet so that the middle note of the triplet will be articulated as a separate note, which is then followed by the A.:

Because the starting and arrival notes are reflected by the notated pitches on the standard stave - showing the shape of the melodic line - the first part of the triplet consists of 2 sixteenth notes instead of 1 eighth note. Those 2 sixteenth notes are therefore the actual bend.

If that seems a bit confusing...
Another way - and closer to what is shown in your images - is to create a unison bend:

See:
https://musescore.org/en/handbook/4/guitar-bends#Adding_bends_to_chords

Those unison noteheads can be combined by changing the notehead direction of the backward-facing E in the Properties panel. Also, allow the bend to sound, but mute the overlapped E so that it doesn't play during the bend. Listen to measure 2 and compare to the others.
Here's the MuseScore file: Bend.mscz

BTW: Use Format > Style > Bends to make the label for full bends show the word "full" instead of "1":