=IFERROR(INDIRECT(TEXT(SMALL(IF(MOD(COLUMN($B$2:$K$2),3)=2,IF($B$2:$K$10=A1,ROW($B$2:$K$10)*1000+COLUMN($B$2:$K$10)+1)), 1 ),"R00C000"),0),"Not Found")
The COLUMN looks at the column of the range, in this case 2-11. The MOD takes the column number, divides by 3 and returns the remainder. If the remainder is 2, it's a column where the lookup value might be found. Since we're dividing by 3, it means every 3rd column gets checked, 2, 5, 8, and 11.
=IFERROR(INDIRECT(TEXT(SMALL(IF(MOD(COLUMN($B$2:$K$2),3)=2,IF($B$2:$K$10=A1,ROW($B$2:$K$10)*1000+COLUMN($B$2:$K$10)+1)), 1 ),"R00C000"),0),"Not Found")
Now that we've restricted the columns to look at, we look at every cell in the range to see if any of them match A1. If any of them do, we take the row number of it, multiply by 1000, then add the column number, and add one more since we want to return the value to the right of the cell that matches. So if the matching cell is E8, the row is 8, the column is 5, so we get 8000 + 5 + 1 = 8006.
=IFERROR(INDIRECT(TEXT(SMALL(IF(MOD(COLUMN($B$2:$K$2),3)=2,IF($B$2:$K$10=A1,ROW($B$2:$K$10)*1000+COLUMN($B$2:$K$10)+1)), 1 ),"R00C000"),0),"Not Found")
The above process will return a 2-dimensional array containing 1 or more matching row/column number values, or a FALSE value for all the cells that do not match. The SMALL returns the least numeric value, which would be the 8006.
=IFERROR(INDIRECT(TEXT(SMALL(IF(MOD(COLUMN($B$2:$K$2),3)=2,IF($B$2:$K$10=A1,ROW($B$2:$K$10)*1000+COLUMN($B$2:$K$10)+1)), 1 ),"R00C000"),0),"Not Found")
The TEXT function formats a value according the the pattern given. In this case, it turns the 8006 to "R8C006". This is the alternate way of describing a cell, instead of F8, you give it the row and column. Then the INDIRECT returns the value at the reference given, and the (blue) zero parameter tells it to use the R1C1 style of referencing.
