Then they shall confess
yadah  (yaw-daw')
cast (out), (make) confess(-ion), praise, shoot, (give) thank(-ful, -s, -sgiving).
their sin
chatta'ah  (khat-taw-aw')
an offence (sometimes habitual sinfulness), and its penalty, occasion, sacrifice, or expiation; also (concretely) an offender
which they have done
`asah  (aw-saw')
to do or make, in the broadest sense and widest application
and he shall recompense
shuwb  (shoob)
to turn back (hence, away) transitively or intransitively, literally or figuratively
his trespass
'asham  (aw-shawm')
guilt; by implication, a fault; also a sin-offering -- guiltiness, (offering for) sin, trespass (offering).
with the principal
ro'sh  (roshe)
the head (as most easily shaken), whether literal or figurative (in many applications, of place, time, rank, itc.)
thereof and add
yacaph  (yaw-saf')
to add or augment (often adverbial, to continue to do a thing)
unto it the fifth
chamiyshiy  (kham-ee-shee')
fifth; also a fifth -- fifth (part).
part thereof and give
nathan  (naw-than')
to give, used with greatest latitude of application (put, make, etc.)
it unto him against whom he hath trespassed
'asham  (aw-sham')
to be guilty; by implication to be punished or perish