To help identify the best way forward, perhaps you could say how many employees there are and what happens when there is a new employee or one leaves. Presumably there is an update to tab 1
Do you want just a formula-based solution or would you consider VBA (Macro)?
As a starter, I have appended a small example workbook using a formula (Vlookup and IF).
The 'COLUMN()' function wihtin it is to select the column from the look-up table based on the position of the column in Tab1. In this example, the first day on Tab2 is in column B (=2)whilst the first day on Tab1 is column D (=4). Thus we need to take 2 off to get the same column. Another reason for using COLUMN() is to avoid having to put in the explicit column number in each VLOOKUP. As it is, with the mix of references, the formula can be copied to each appropriate cell.
There are quite a few pitfalls - any change to the number of rows in Tab2 requires the formula to be rewritten. (Ideally use a range name.) It assumes that the days are in the same order and that the 'R' is always upper case. I probably would not use this myself for more than say 100 employees but instead go to a macro to find the record, copy the data and delete the shift patterns.
Hope this helps (if so remember the star!)