Need help with excel

Here's a couple additional options for MS365...

Shift columns:

=LET(
   tbl, A2:N6,
   rng, DROP(tbl,1),
   beg, INDEX(rng,,1),
   end, INDEX(rng,,2),
   val, DROP(rng,,2),
   low, MIN(beg),
   upp, MAX(end),
   fnλ, LAMBDA(b,e,(YEAR(e)-YEAR(b))*12+MONTH(e)-MONTH(b)),
   dur, fnλ(beg,end)+1,
   num, SEQUENCE(,fnλ(low,upp)+1,0),
   hdr, EOMONTH(low,num),
   cId, 1+num-fnλ(low,beg),
   rId, SEQUENCE(ROWS(rng)),
   arr, IF((cId>0)*(cId<=dur),INDEX(val,rId,cId),""),
   HSTACK(TAKE(tbl,,2),VSTACK(hdr,arr))
)

Unpivot/repivot:

=LET(
   tbl, A2:N6,
   rng, DROP(tbl,1),
   beg, INDEX(rng,,1),
   end, INDEX(rng,,2),
   val, DROP(rng,,2),
   dur, (YEAR(end)-YEAR(beg))*12+MONTH(end)-MONTH(beg)+1,
   num, SEQUENCE(,COLUMNS(val),0),
   arr, IFS(num<dur,EOMONTH(+beg,num)),
   err, ISERROR(arr),
   rId, SEQUENCE(ROWS(rng)),
   pvt, PIVOTBY(TOCOL(IF(err,arr,rId),2),TOCOL(arr,2),TOCOL(IF(err,arr,val),2),SINGLE,0,0,,0),
   HSTACK(VSTACK(TAKE(tbl,1,2),INDEX(rng,TAKE(DROP(pvt,1),,1),{1,2})),DROP(pvt,,1))
)

See attached...