I used the calculated dimension of:
=if(Title='Trainee' or Title='Others-Legal', null(), Title) and checked the surpess when value is null option
The trainee and Others-legal titles are removed from the chart, but the figures for the remaining values are changed as a result. The chart below shows the outcome.
The same is true when using the restriction in the expression. What I am looking to do is to remove those titles and still keep the original values - as per the original figures on the chart picture in my original post.