how to disable text box based on values from dropbox

i have a model like follows

public partial class CanditateReference
    {

 public titles? CanditateRelationToRef1 { get; set; }
        public string? CanditateReference1Relation { get; set; }

 public enum titles
        {
            select,
            Manager,
            Others
        }

}

i am populating the values in dropdown from enum .

What i am tring to do is if in the dropdown others is selected there is a text box named others which should be enabled , rest of the time it should be disbaled 

what i tried is