[Stefan]

user wrote:

FROM:
GROUP1{TAB}IT{TAB}EM1{TAB}SENT
GROUP1{TAB}I{TAB}TE M2{TAB}SENT
GROUP2{TAB}IT E M3{TAB}SENT
GROUP2{TAB}ITE{TAB}M4{TAB}NOT SENT
GROUP2{TAB}ITEM5{TAB}SENT

TO:
GROUP1{TAB}SENT
GROUP2{TAB}NOT SENT

Try (with an copy of your file!)
this RegEx search & replace:

FIND: (.+?t).+t(NOT SENT|SENT)
REPL: $1$2
[X] Use Regular Expressions

Explanation:
(.+?t) = match and store all non-greedy till the first TAB into group $1
.+ = match all, but only till:
t(NOT SENT|SENT) = an TAB followed by “not sent” OR “sent”, which ever is stored in $2

.