How to change 'Placeholder' name and 'Mat-label' heading name with selection of a name from previous dropdown field

[p revanth]

-> Here I have two fields one is drop-down and one is input fields.

-> After the user selects the first field for example if he selects 'father of' from the first field then the second field placeholder and mat label should change to 'father of' like this, it should change for every selection

-> I tried to implement by using boolean values but it is not getting for me please look at my code and help me through stackblitz

Link of stackoverflow for detail question: https://stackoverflow.com/questions/69793039/how-to-change-placeholder-name-and-mat-label-heading-name-with-selection-of