Here's how to clear all markers in Premiere Pro.
Step 1:
Select your timeline by clicking on it.
Step 2:
Right-click in the top area above the yellow timeline line.
Step 3:
Select "Clear Markers" from the menu.
All markers are now removed from your timeline. Note: This action clears all markers at once and cannot be undone. Make sure to save your project before clearing if you might need any marker information later.