Time Zone Conversion Button

In the spreadsheet attached , I have four buttons which needs some macros to perform below function -

IF button 1 is clicked - It should assume that Data is in IST format and should convert it to PST format
IF button 2 is clicked - It should assume that data is in EST format and should convert it to PST format ..
Similarily for other tabs as well.

Actually the data will not be fixed , data keeps getting added to this . So the macro needs to check until last row and convert all of them .