How to get value portion key to every rn from 1 to 3 row on one row?

Question

I need to get value portion key to every 3 row on one row meaning

rn 1,2,3 one row KRM__21X0E100C0ADD

rn 1,2,3 one row KRM__21X0J100K0ADD

rn 1,2,3 on one row KRM__21X1C100D0ADD

create table #portiontableFinal
(
rn int,
ValuePortionKey nvarchar(100)
)
insert into #portiontableFinal(rn,ValuePortionKey)
values
(1,'KRM__21X0E100'),
(2,'C0AD'),
(3,'D'),
(1,'KRM__21X0J100'),
(2,'K0AD'),
(3,'D'),
(1,'KRM__21X1C100'),
(2,'D0AD'),
(3,'D')
RN  ValuePortionKey
1   KRM__21X0E100
2   C0AD
3   D
1   KRM__21X0J100
2   K0AD
3   D
1   KRM__21X1C100
2   D0AD
3   D

I need to get from 1 to 3 on one rows as following :

final result I need to get as below :

KRM__21X0E100C0ADD

KRM__21X0J100K0ADD

KRM__21X1C100D0ADD