Changing the line style in MicroStation is a relatively simple process. Here is a short guide to help you get started:
Open the element you need to modify, such as a line or a shape.
Select the Details tab in the Element Information dialog.
In the Properties section, select the Line Type field.
Select the line type that you need from the drop-down list.
Click the OK button to apply the changes to the element.
If you need more detailed instructions on how to change the line type in MicroStation, you can find them here: https://knowledge.bentley.com/display/PUBL/Changing+Line+Styles.
Hopefully, this answer has helped you learn how to modify the line style in MicroStation. Let me know if you have any more questions about it!