Try this — 
T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1085430/kpmarch.xlsx')
T1 = 744×6 table
           OBSR_YMD            A_VALUE        OBSRVT_NM         K_VALUE        CRT_DT            OBSR_VYMD     
    _______________________    _______    __________________    _______    ______________    __________________
    {'2022-03-31 21:00:00'}    {'27'}     {'Planetary'     }     {'2'}     {'2022-04-30'}    {'20220331210000'}
    {'2022-03-31 21:00:00'}    {'18'}     {'Fredericksburg'}     {'2'}     {'2022-04-30'}    {'20220331210000'}
    {'2022-03-31 21:00:00'}    {'35'}     {'College'       }     {'2'}     {'2022-04-30'}    {'20220331210000'}
    {'2022-03-31 18:00:00'}    {'27'}     {'Planetary'     }     {'4'}     {'2022-04-30'}    {'20220331180000'}
    {'2022-03-31 18:00:00'}    {'18'}     {'Fredericksburg'}     {'3'}     {'2022-04-30'}    {'20220331180000'}
    {'2022-03-31 18:00:00'}    {'35'}     {'College'       }     {'4'}     {'2022-04-30'}    {'20220331180000'}
    {'2022-03-31 15:00:00'}    {'27'}     {'Planetary'     }     {'4'}     {'2022-04-30'}    {'20220331150000'}
    {'2022-03-31 15:00:00'}    {'18'}     {'Fredericksburg'}     {'4'}     {'2022-04-30'}    {'20220331150000'}
    {'2022-03-31 15:00:00'}    {'35'}     {'College'       }     {'4'}     {'2022-04-30'}    {'20220331150000'}
    {'2022-03-31 12:00:00'}    {'27'}     {'Planetary'     }     {'4'}     {'2022-04-30'}    {'20220331120000'}
    {'2022-03-31 12:00:00'}    {'18'}     {'Fredericksburg'}     {'3'}     {'2022-04-30'}    {'20220331120000'}
    {'2022-03-31 12:00:00'}    {'35'}     {'College'       }     {'6'}     {'2022-04-30'}    {'20220331120000'}
    {'2022-03-31 09:00:00'}    {'27'}     {'Planetary'     }     {'4'}     {'2022-04-30'}    {'20220331090000'}
    {'2022-03-31 09:00:00'}    {'18'}     {'Fredericksburg'}     {'3'}     {'2022-04-30'}    {'20220331090000'}
    {'2022-03-31 09:00:00'}    {'35'}     {'College'       }     {'5'}     {'2022-04-30'}    {'20220331090000'}
    {'2022-03-31 06:00:00'}    {'27'}     {'Planetary'     }     {'5'}     {'2022-04-30'}    {'20220331060000'}
Lv = ismember(T1{:,3},'Planetary');
Result = T1(Lv,[1 3 4])
Result = 248×3 table
           OBSR_YMD              OBSRVT_NM      K_VALUE
    _______________________    _____________    _______
    {'2022-03-31 21:00:00'}    {'Planetary'}     {'2'} 
    {'2022-03-31 18:00:00'}    {'Planetary'}     {'4'} 
    {'2022-03-31 15:00:00'}    {'Planetary'}     {'4'} 
    {'2022-03-31 12:00:00'}    {'Planetary'}     {'4'} 
    {'2022-03-31 09:00:00'}    {'Planetary'}     {'4'} 
    {'2022-03-31 06:00:00'}    {'Planetary'}     {'5'} 
    {'2022-03-31 03:00:00'}    {'Planetary'}     {'5'} 
    {'2022-03-31 00:00:00'}    {'Planetary'}     {'4'} 
    {'2022-03-30 21:00:00'}    {'Planetary'}     {'2'} 
    {'2022-03-30 18:00:00'}    {'Planetary'}     {'2'} 
    {'2022-03-30 15:00:00'}    {'Planetary'}     {'1'} 
    {'2022-03-30 12:00:00'}    {'Planetary'}     {'2'} 
    {'2022-03-30 09:00:00'}    {'Planetary'}     {'1'} 
    {'2022-03-30 06:00:00'}    {'Planetary'}     {'1'} 
    {'2022-03-30 03:00:00'}    {'Planetary'}     {'1'} 
    {'2022-03-30 00:00:00'}    {'Planetary'}     {'2'} 
There are likely also other approaches.  
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