It sounds like you might be using slurs and ties interchangeably, but they’re not the same, neither musically nor in Dorico. A slur indicates that notes should be played legato, or in a single bow movement, or similar; those notes are normally, though not always, different pitches, but they will always be re-articulated, at least to some degree. A tie, on the other hand, indicates a single attack, and you do not hear any re-articulation corresponding to subsequent noteheads in the tie. To create a slur, you use S. To create a tie, you use T. See this page for more information.