There are lots of options for how rhythms are displayed, in the Write menu, Notation Options, Note Grouping.
However your example is one that “slips through the cracks” in the options, and you have to do it manually.
Enter the four 8th-notes, press T for the tie, press O for “force duration” (or click the “G-clamp” icon in the left hand panel), then enter the dotted quarter note.
Then press O again to cancel the force duration, otherwise Dorico will notate everything exactly as you input it, and that might not be a good idea if you copy and paste the music to a different part of a bar later on, for example.
You can also fix this by editing the music after you entered it.
Select the tied notes and press U to “untie” them. Select the first 8th note and press O to set forced duration. Then select the quarter note and press “.” to convert it into a dotted quarter. Then go back to the first 8th note and press T to replace the tie.
It’s a lot quicker to actually do it than to explain it!